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/aos/controls/BUILD b/aos/controls/BUILD
index 7172cbb..14890d4 100644
--- a/aos/controls/BUILD
+++ b/aos/controls/BUILD
@@ -1,7 +1,6 @@
 package(default_visibility = ["//visibility:public"])
 
 load("@com_github_google_flatbuffers//:build_defs.bzl", "flatbuffer_cc_library")
-load("//tools:environments.bzl", "mcu_cpus")
 
 cc_library(
     name = "control_loop_test",
@@ -12,6 +11,7 @@
     hdrs = [
         "control_loop_test.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos:flatbuffers",
         "//aos:json_to_flatbuffer",
@@ -25,27 +25,20 @@
 )
 
 cc_library(
-    name = "polytope_uc",
-    hdrs = [
-        "polytope.h",
-    ],
-    restricted_to = mcu_cpus,
-    deps = [
-        "@org_tuxfamily_eigen//:eigen",
-    ],
-)
-
-cc_library(
     name = "polytope",
     hdrs = [
         "polytope.h",
     ],
     deps = [
-        "//aos/logging",
-        "//third_party/cddlib",
-        "@com_github_google_glog//:glog",
         "@org_tuxfamily_eigen//:eigen",
-    ],
+    ] + select({
+        "@platforms//os:linux": [
+            "//aos/logging",
+            "//third_party/cddlib",
+            "@com_github_google_glog//:glog",
+        ],
+        "//conditions:default": [],
+    }),
 )
 
 cc_test(
@@ -53,6 +46,7 @@
     srcs = [
         "polytope_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":polytope",
         "//aos/testing:googletest",
@@ -66,6 +60,7 @@
     srcs = [
         "control_loops.fbs",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
 )
 
 cc_library(
@@ -77,6 +72,7 @@
     hdrs = [
         "control_loop.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos/events:event_loop",
         "//aos/events:shm_event_loop",
@@ -96,6 +92,7 @@
     hdrs = [
         "quaternion_utils.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "@com_github_google_glog//:glog",
         "@org_tuxfamily_eigen//:eigen",
@@ -107,6 +104,7 @@
     srcs = [
         "quaternion_utils_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":quaternion_utils",
         "//aos/testing:googletest",