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/y2020/vision/tools/python_code/BUILD b/y2020/vision/tools/python_code/BUILD
index 9b4eb08..4ff3397 100644
--- a/y2020/vision/tools/python_code/BUILD
+++ b/y2020/vision/tools/python_code/BUILD
@@ -1,4 +1,5 @@
 load("@com_github_google_flatbuffers//:build_defs.bzl", "flatbuffer_cc_library", "flatbuffer_py_library")
+load("//tools:platforms.bzl", "platforms")
 
 py_binary(
     name = "load_sift_training",
@@ -17,6 +18,7 @@
     ]),
     python_version = "PY3",
     srcs_version = "PY2AND3",
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//external:python-glog",
         "//y2020/vision/sift:sift_fbs_python",
@@ -34,6 +36,7 @@
         "$(location :load_sift_training)",
         "$(location sift_training_data.h)",
     ]),
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         ":load_sift_training",
     ],
@@ -44,6 +47,7 @@
     hdrs = [
         "sift_training_data.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
 
@@ -63,9 +67,10 @@
     data = glob(["calib_files/*.json"]) + glob([
         "test_images/*.png",
     ]),
-    python_version = "PY3",
     main = "load_sift_training.py",
+    python_version = "PY3",
     srcs_version = "PY2AND3",
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":load_sift_training",
         "//external:python-glog",
@@ -84,6 +89,7 @@
         "$(location :load_sift_training_test)",
         "$(location sift_training_data_test.h) test",
     ]),
+    target_compatible_with = ["@platforms//os:linux"],
     tools = [
         ":load_sift_training_test",
     ],
@@ -94,6 +100,7 @@
     hdrs = [
         "sift_training_data_test.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
 )
 
@@ -102,10 +109,7 @@
     srcs = [
         "camera_param_test.cc",
     ],
-    restricted_to = [
-        "//tools:k8",
-        "//tools:armhf-debian",
-    ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":sift_training_data_test",
         "//aos/testing:googletest",