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/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",