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/third_party/allwpilib/BUILD b/third_party/allwpilib/BUILD
index 61f6098..bee2e64 100644
--- a/third_party/allwpilib/BUILD
+++ b/third_party/allwpilib/BUILD
@@ -34,6 +34,7 @@
     srcs = [
         "generate_FRCUsageReporting.py",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 genrule(
@@ -53,6 +54,7 @@
         "$(location hal/src/generate/ResourceType.txt)",
         "$(location hal/src/main/native/include/hal/FRCUsageReporting.h)",
     ]),
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         ":generate_FRCUsageReporting",
     ],
@@ -79,7 +81,7 @@
         "-Wno-cast-align",
     ],
     includes = _hal_header_dirs,
-    restricted_to = ["//tools:roborio"],
+    target_compatible_with = ["//tools/platforms/hardware:roborio"],
     visibility = ["//third_party:__pkg__"],
     deps = [
         "//aos/logging",
diff --git a/third_party/allwpilib/wpiutil/BUILD b/third_party/allwpilib/wpiutil/BUILD
index 98ed173..8c1b8db 100644
--- a/third_party/allwpilib/wpiutil/BUILD
+++ b/third_party/allwpilib/wpiutil/BUILD
@@ -23,6 +23,6 @@
     includes = [
         "src/main/native/include",
     ],
-    restricted_to = ["//tools:roborio"],
+    target_compatible_with = ["//tools/platforms/hardware:roborio"],
     visibility = ["//visibility:public"],
 )