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/BUILD b/y2014/BUILD
index c77a019..4332a63 100644
--- a/y2014/BUILD
+++ b/y2014/BUILD
@@ -9,6 +9,7 @@
     hdrs = [
         "constants.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//aos/logging",
@@ -26,6 +27,7 @@
     srcs = [
         "joystick_reader.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":constants",
         "//aos:init",
@@ -55,6 +57,7 @@
         "//y2014/control_loops/shooter:shooter",
         "//y2014/actors:binaries",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_binary(
@@ -62,6 +65,7 @@
     srcs = [
         "hot_goal_reader.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos:byteorder",
         "//aos:init",
@@ -85,6 +89,7 @@
         "//y2014/control_loops/claw:claw_position_fbs",
         "//y2014/control_loops/claw:claw_status_fbs",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//aos/robot_state:config",
@@ -97,7 +102,7 @@
     srcs = [
         "wpilib_interface.cc",
     ],
-    restricted_to = ["//tools:roborio"],
+    target_compatible_with = ["//tools/platforms/hardware:roborio"],
     deps = [
         ":constants",
         "//aos:init",
@@ -139,5 +144,6 @@
 py_library(
     name = "python_init",
     srcs = ["__init__.py"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )