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/y2014_bot3/BUILD b/y2014_bot3/BUILD
index 6d1f3fd..c2a1793 100644
--- a/y2014_bot3/BUILD
+++ b/y2014_bot3/BUILD
@@ -5,6 +5,7 @@
     srcs = [
         "joystick_reader.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos:init",
         "//aos/actions:action_lib",
@@ -27,6 +28,7 @@
         "//y2014_bot3/control_loops/drivetrain:drivetrain",
         "//y2014_bot3/control_loops/rollers:rollers",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_binary(
@@ -34,7 +36,7 @@
     srcs = [
         "wpilib_interface.cc",
     ],
-    restricted_to = ["//tools:roborio"],
+    target_compatible_with = ["//tools/platforms/hardware:roborio"],
     deps = [
         "//aos:init",
         "//aos:make_unique",
@@ -68,5 +70,6 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
diff --git a/y2014_bot3/actors/BUILD b/y2014_bot3/actors/BUILD
index ad60458..d90d388 100644
--- a/y2014_bot3/actors/BUILD
+++ b/y2014_bot3/actors/BUILD
@@ -6,6 +6,7 @@
     hdrs = [
         "autonomous_actor.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos/actions:action_lib",
         "//aos/events:event_loop",
@@ -22,6 +23,7 @@
     srcs = [
         "autonomous_actor_main.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":autonomous_action_lib",
diff --git a/y2014_bot3/control_loops/BUILD b/y2014_bot3/control_loops/BUILD
index 8df2481..30fb1ec 100644
--- a/y2014_bot3/control_loops/BUILD
+++ b/y2014_bot3/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 = ["//y2014_bot3:python_init"],
 )
diff --git a/y2014_bot3/control_loops/drivetrain/BUILD b/y2014_bot3/control_loops/drivetrain/BUILD
index 7060ac1..9a5bb53 100644
--- a/y2014_bot3/control_loops/drivetrain/BUILD
+++ b/y2014_bot3/control_loops/drivetrain/BUILD
@@ -9,6 +9,7 @@
         "kalman_drivetrain_motor_plant.cc",
     ],
     cmd = "$(location //y2014_bot3/control_loops/python:drivetrain) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2014_bot3/control_loops/python:drivetrain",
     ],
@@ -26,6 +27,7 @@
         "hybrid_velocity_drivetrain.cc",
     ],
     cmd = "$(location //y2014_bot3/control_loops/python:polydrivetrain) $(OUTS)",
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         "//y2014_bot3/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",
@@ -72,6 +76,7 @@
     srcs = [
         "drivetrain_main.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":drivetrain_base",
         "//aos:init",
diff --git a/y2014_bot3/control_loops/python/BUILD b/y2014_bot3/control_loops/python/BUILD
index 83e7bba..b63ca0a 100644
--- a/y2014_bot3/control_loops/python/BUILD
+++ b/y2014_bot3/control_loops/python/BUILD
@@ -6,7 +6,7 @@
         "drivetrain.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":python_init",
         "//external:python-gflags",
@@ -22,7 +22,7 @@
         "polydrivetrain.py",
     ],
     legacy_create_init = False,
-    restricted_to = ["//tools:k8"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":python_init",
         "//external:python-gflags",
@@ -34,6 +34,7 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = ["//y2014_bot3/control_loops:python_init"],
 )
diff --git a/y2014_bot3/control_loops/rollers/BUILD b/y2014_bot3/control_loops/rollers/BUILD
index e0d7dc6..2f9d7c4 100644
--- a/y2014_bot3/control_loops/rollers/BUILD
+++ b/y2014_bot3/control_loops/rollers/BUILD
@@ -8,6 +8,7 @@
         "rollers_goal.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 flatbuffer_cc_library(
@@ -16,6 +17,7 @@
         "rollers_position.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 flatbuffer_cc_library(
@@ -24,6 +26,7 @@
         "rollers_output.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 flatbuffer_cc_library(
@@ -32,6 +35,7 @@
         "rollers_status.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_library(
@@ -42,6 +46,7 @@
     hdrs = [
         "rollers.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":rollers_goal_fbs",
         ":rollers_output_fbs",
@@ -57,6 +62,7 @@
     srcs = [
         "rollers_main.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":rollers_lib",
         "//aos:init",