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/y2019/BUILD b/y2019/BUILD
index ddc0a19..3f361a7 100644
--- a/y2019/BUILD
+++ b/y2019/BUILD
@@ -18,6 +18,7 @@
         "//y2019/actors:binaries",
         "//y2019/vision/server",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_library(
@@ -28,6 +29,7 @@
     hdrs = [
         "constants.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//aos/logging",
@@ -54,7 +56,7 @@
     ],
     # This library uses some deprecated parts of the SPI API.
     copts = ["-Wno-deprecated-declarations"],
-    restricted_to = ["//tools:roborio"],
+    target_compatible_with = ["//tools/platforms/hardware:roborio"],
     deps = [
         ":camera_log_fbs",
         ":constants",
@@ -103,6 +105,7 @@
     hdrs = [
         "joystick_angle.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos/input:drivetrain_input",
         "//frc971/zeroing:wrap",
@@ -114,6 +117,7 @@
     srcs = [
         "joystick_angle_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":joystick_angle",
         "//aos/testing:googletest",
@@ -125,6 +129,7 @@
     srcs = [
         ":joystick_reader.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":camera_log_fbs",
         ":vision_proto",
@@ -158,6 +163,7 @@
         "camera_log.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
 
@@ -167,6 +173,7 @@
         "status_light.fbs",
     ],
     gen_reflections = 1,
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
 
@@ -183,6 +190,7 @@
         "//y2019/control_loops/superstructure:superstructure_status_fbs",
         ":camera_log_fbs",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//aos/robot_state:config",
@@ -195,11 +203,13 @@
 cc_proto_library(
     name = "vision_proto",
     srcs = ["vision.proto"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
 
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )