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/y2012/BUILD b/y2012/BUILD
index ff6d3f2..cc0a406 100644
--- a/y2012/BUILD
+++ b/y2012/BUILD
@@ -5,6 +5,7 @@
     srcs = [
         "joystick_reader.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos:init",
         "//aos/actions:action_lib",
@@ -26,6 +27,7 @@
         "//y2012/control_loops/drivetrain",
         "//y2012/control_loops/accessories",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_binary(
@@ -33,7 +35,7 @@
     srcs = [
         "wpilib_interface.cc",
     ],
-    restricted_to = ["//tools:roborio"],
+    target_compatible_with = ["//tools/platforms/hardware:roborio"],
     deps = [
         "//aos:init",
         "//aos:make_unique",
@@ -70,5 +72,6 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
diff --git a/y2012/control_loops/BUILD b/y2012/control_loops/BUILD
index 613ddd4..1cf6e97 100644
--- a/y2012/control_loops/BUILD
+++ b/y2012/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 = ["//y2012:python_init"],
 )
diff --git a/y2012/control_loops/accessories/BUILD b/y2012/control_loops/accessories/BUILD
index 65a6d1d..02a15f1 100644
--- a/y2012/control_loops/accessories/BUILD
+++ b/y2012/control_loops/accessories/BUILD
@@ -7,6 +7,7 @@
     srcs = [
         "accessories.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":accessories_fbs",
         "//aos:init",
@@ -20,4 +21,5 @@
     srcs = [
         "accessories.fbs",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
diff --git a/y2012/control_loops/drivetrain/BUILD b/y2012/control_loops/drivetrain/BUILD
index 35d596a..cd575ea 100644
--- a/y2012/control_loops/drivetrain/BUILD
+++ b/y2012/control_loops/drivetrain/BUILD
@@ -9,6 +9,7 @@
         "kalman_drivetrain_motor_plant.cc",
     ],
     cmd = "$(location //y2012/control_loops/python:drivetrain) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2012/control_loops/python:drivetrain",
     ],
@@ -26,6 +27,7 @@
         "hybrid_velocity_drivetrain.cc",
     ],
     cmd = "$(location //y2012/control_loops/python:polydrivetrain) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2012/control_loops/python:polydrivetrain",
     ],
@@ -46,6 +48,7 @@
         "kalman_drivetrain_motor_plant.h",
         "polydrivetrain_dog_motor_plant.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//frc971/control_loops:hybrid_state_feedback_loop",
         "//frc971/control_loops:state_feedback_loop",
@@ -60,6 +63,7 @@
     hdrs = [
         "drivetrain_base.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":polydrivetrain_plants",
         "//frc971:shifter_hall_effect",
@@ -73,6 +77,7 @@
     srcs = [
         "drivetrain_main.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":drivetrain_base",
         "//aos:init",
diff --git a/y2012/control_loops/python/BUILD b/y2012/control_loops/python/BUILD
index f10d6fa..1bceece 100644
--- a/y2012/control_loops/python/BUILD
+++ b/y2012/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"],
     deps = [
         "//external:python-gflags",
         "//external:python-glog",
@@ -48,6 +48,7 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = ["//y2012/control_loops:python_init"],
 )