Switch everything to platforms

This patch switches the codebase over from using the "cpu"
mechanism to using bazel platforms. See
https://docs.bazel.build/versions/master/platforms.html for some more
information.

Most of the substantial changes are in //tools. Instead of using
`cc_toolchain_suite` rules, we now use regular `toolchain` rules that
are registered in the WORKSPACE. That also means that bazel now uses
the target platform to select the compiler.

All --cpu=* arguments should now be --config=* arguments. For example,
`--cpu=roborio` should now be `--config=roborio`. The CI script and
all documentation has been updated to reflect that.

The remainder of the changes revolve around tagging all targets with
`target_compatible_with`.  The old mechanism allowed us to specify
repo-wide defaults. The new mechanism does not. That means every
target that didn't have any compatibility specified, now requires
compatibility with `@platforms//os:linux`.

I used buildozer for the vast majority of `target_compatible_with`
changes. buildozer automatically buildifies any BUILD files it
touches. That means this patch also contains a few non-functional
changes that I was too lazy to remove.

Change-Id: I66d6e6ad9161520ee397597cdb492585820a3acd
diff --git a/y2018/control_loops/BUILD b/y2018/control_loops/BUILD
index 57f2864..90a398e 100644
--- a/y2018/control_loops/BUILD
+++ b/y2018/control_loops/BUILD
@@ -1,6 +1,7 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = ["//y2018:python_init"],
 )
diff --git a/y2018/control_loops/drivetrain/BUILD b/y2018/control_loops/drivetrain/BUILD
index 4d6a6a1..e9a75b8 100644
--- a/y2018/control_loops/drivetrain/BUILD
+++ b/y2018/control_loops/drivetrain/BUILD
@@ -7,6 +7,7 @@
         "kalman_drivetrain_motor_plant.cc",
     ],
     cmd = "$(location //y2018/control_loops/python:drivetrain) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2018/control_loops/python:drivetrain",
     ],
@@ -23,6 +24,7 @@
         "hybrid_velocity_drivetrain.cc",
     ],
     cmd = "$(location //y2018/control_loops/python:polydrivetrain) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2018/control_loops/python:polydrivetrain",
     ],
@@ -42,6 +44,7 @@
         "kalman_drivetrain_motor_plant.h",
         "polydrivetrain_dog_motor_plant.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//frc971/control_loops:hybrid_state_feedback_loop",
@@ -57,6 +60,7 @@
     hdrs = [
         "drivetrain_base.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":polydrivetrain_plants",
@@ -70,6 +74,7 @@
     srcs = [
         "drivetrain_main.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":drivetrain_base",
diff --git a/y2018/control_loops/python/BUILD b/y2018/control_loops/python/BUILD
index 7cea41b..1f29601 100644
--- a/y2018/control_loops/python/BUILD
+++ b/y2018/control_loops/python/BUILD
@@ -6,7 +6,7 @@
         "drivetrain.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":python_init",
         "//external:python-gflags",
@@ -22,7 +22,7 @@
         "polydrivetrain.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":python_init",
         "//external:python-gflags",
@@ -37,7 +37,7 @@
         "drivetrain.py",
         "polydrivetrain.py",
     ],
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     visibility = ["//visibility:public"],
     deps = [
         ":python_init",
@@ -55,7 +55,7 @@
         "polydrivetrain_test.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":polydrivetrain_lib",
         ":python_init",
@@ -73,7 +73,7 @@
         "path_points.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":python_init",
         "//external:python-gflags",
@@ -88,7 +88,7 @@
         "intake.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":python_init",
         "//external:python-gflags",
@@ -103,6 +103,7 @@
     hdrs = [
         "dlqr.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "@slycot_repo//:slicot",
     ],
@@ -113,7 +114,7 @@
     srcs = [
         "arm_mpc.cc",
     ],
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":arm_bounds",
         ":dlqr",
@@ -129,7 +130,7 @@
     srcs = [
         "3d_plot.cc",
     ],
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":arm_bounds",
         "//third_party/matplotlib-cpp",
@@ -145,6 +146,7 @@
     hdrs = [
         "arm_bounds.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "@cgal_repo//:cgal",
         "@org_tuxfamily_eigen//:eigen",
@@ -156,7 +158,7 @@
     srcs = [
         "2d_plot.cc",
     ],
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         "//third_party/matplotlib-cpp",
         "@com_github_gflags_gflags//:gflags",
@@ -169,10 +171,10 @@
         "graph_edit.py",
         "graph_generate.py",
     ],
-    python_version = "PY3",
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    python_version = "PY3",
     srcs_version = "PY3",
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":python_init",
         "//frc971/control_loops/python:basic_window",
@@ -187,9 +189,10 @@
         "graph_codegen.py",
         "graph_generate.py",
     ],
-    python_version = "PY2",
     legacy_create_init = False,
+    python_version = "PY2",
     srcs_version = "PY2",
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":python_init",
     ],
@@ -198,6 +201,7 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = ["//y2018/control_loops:python_init"],
 )
@@ -207,7 +211,7 @@
     srcs = [
         "extended_lqr.py",
     ],
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         "//external:python-gflags",
         "//external:python-glog",
@@ -221,7 +225,7 @@
         "arm_mpc.py",
     ],
     main = "arm_mpc.py",
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         "//external:python-gflags",
         "//external:python-glog",
diff --git a/y2018/control_loops/superstructure/BUILD b/y2018/control_loops/superstructure/BUILD
index db01298..d44807e 100644
--- a/y2018/control_loops/superstructure/BUILD
+++ b/y2018/control_loops/superstructure/BUILD
@@ -11,6 +11,7 @@
     includes = [
         "//frc971/control_loops:control_loops_fbs_includes",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 flatbuffer_cc_library(
@@ -22,6 +23,7 @@
     includes = [
         "//frc971/control_loops:control_loops_fbs_includes",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 flatbuffer_cc_library(
@@ -33,6 +35,7 @@
     includes = [
         "//frc971/control_loops:control_loops_fbs_includes",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 flatbuffer_cc_library(
@@ -41,6 +44,7 @@
         "superstructure_output.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_library(
@@ -51,6 +55,7 @@
     hdrs = [
         "superstructure.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":superstructure_goal_fbs",
         ":superstructure_output_fbs",
@@ -76,6 +81,7 @@
     ],
     data = ["//y2018:config"],
     shard_count = 5,
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":superstructure_goal_fbs",
         ":superstructure_lib",
@@ -97,6 +103,7 @@
     srcs = [
         "superstructure_main.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":superstructure_lib",
         "//aos:init",
@@ -111,6 +118,7 @@
     hdrs = [
         "debouncer.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_test(
@@ -118,6 +126,7 @@
     srcs = [
         "debouncer_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":debouncer",
         "//aos/testing:googletest",
diff --git a/y2018/control_loops/superstructure/arm/BUILD b/y2018/control_loops/superstructure/arm/BUILD
index bf3c306..d05c245 100644
--- a/y2018/control_loops/superstructure/arm/BUILD
+++ b/y2018/control_loops/superstructure/arm/BUILD
@@ -6,6 +6,7 @@
     hdrs = [
         "trajectory.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":dynamics",
@@ -21,6 +22,7 @@
     srcs = [
         "trajectory_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":demo_path",
         ":dynamics",
@@ -39,6 +41,7 @@
     hdrs = [
         "dynamics.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//frc971/control_loops:runge_kutta",
@@ -53,6 +56,7 @@
         "demo_path.cc",
     ],
     hdrs = ["demo_path.h"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [":trajectory"],
 )
 
@@ -61,6 +65,7 @@
     srcs = [
         "dynamics_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":dynamics",
         "//aos/testing:googletest",
@@ -72,7 +77,7 @@
     srcs = [
         "trajectory_plot.cc",
     ],
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//cpu:x86_64"],
     deps = [
         ":ekf",
         ":generated_graph",
@@ -91,6 +96,7 @@
     hdrs = [
         "ekf.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":dynamics",
@@ -103,11 +109,13 @@
     name = "graph",
     srcs = ["graph.cc"],
     hdrs = ["graph.h"],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_test(
     name = "graph_test",
     srcs = ["graph_test.cc"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":graph",
         "//aos/testing:googletest",
@@ -122,6 +130,7 @@
     hdrs = [
         "arm.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":demo_path",
@@ -143,6 +152,7 @@
         "generated_graph.cc",
     ],
     cmd = "$(location //y2018/control_loops/python:graph_codegen) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2018/control_loops/python:graph_codegen",
     ],
@@ -157,6 +167,7 @@
     copts = [
         "-O1",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":graph",
diff --git a/y2018/control_loops/superstructure/intake/BUILD b/y2018/control_loops/superstructure/intake/BUILD
index dde7c63..c49b80b 100644
--- a/y2018/control_loops/superstructure/intake/BUILD
+++ b/y2018/control_loops/superstructure/intake/BUILD
@@ -7,6 +7,7 @@
         "intake_delayed_plant.cc",
     ],
     cmd = "$(location //y2018/control_loops/python:intake) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2018/control_loops/python:intake",
     ],
@@ -22,6 +23,7 @@
         "intake_delayed_plant.h",
         "intake_plant.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//frc971/control_loops:state_feedback_loop",
@@ -36,6 +38,7 @@
     hdrs = [
         "intake.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":intake_plants",