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/ipc_lib/BUILD b/aos/ipc_lib/BUILD
index 0fb307a..7799cdc 100644
--- a/aos/ipc_lib/BUILD
+++ b/aos/ipc_lib/BUILD
@@ -9,6 +9,7 @@
     linkopts = [
         "-lpthread",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "//aos:macros",
@@ -27,6 +28,7 @@
     hdrs = [
         "core_lib.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":aos_sync",
@@ -45,6 +47,7 @@
     linkopts = [
         "-lrt",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":aos_sync",
@@ -61,6 +64,7 @@
     hdrs = [
         "shared_mem_types.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":aos_sync",
     ],
@@ -74,6 +78,7 @@
     tags = [
         "manual",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":core_lib",
         "//aos:die",
@@ -93,6 +98,7 @@
         "ipc_comparison.cc",
     ],
     linkopts = ["-lrt"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos:condition",
         "//aos:event",
@@ -112,6 +118,7 @@
     hdrs = [
         "signalfd.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "@com_github_google_glog//:glog",
@@ -123,6 +130,7 @@
     srcs = [
         "signalfd_test.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":signalfd",
         "//aos/testing:googletest",
@@ -135,6 +143,7 @@
     name = "index",
     srcs = ["index.cc"],
     hdrs = ["index.h"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "@com_github_google_glog//:glog",
@@ -144,6 +153,7 @@
 cc_test(
     name = "index_test",
     srcs = ["index_test.cc"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":index",
         "//aos/testing:googletest",
@@ -158,6 +168,7 @@
         "lockless_queue_memory.h",
     ],
     hdrs = ["lockless_queue.h"],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":aos_sync",
@@ -181,6 +192,7 @@
     hdrs = [
         "queue_racer.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":lockless_queue",
         "//aos:event",
@@ -192,6 +204,7 @@
     name = "lockless_queue_test",
     timeout = "eternal",
     srcs = ["lockless_queue_test.cc"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":lockless_queue",
         ":queue_racer",
@@ -206,6 +219,7 @@
 cc_test(
     name = "lockless_queue_death_test",
     srcs = ["lockless_queue_death_test.cc"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":lockless_queue",
         ":queue_racer",
@@ -224,6 +238,7 @@
     hdrs = [
         "data_alignment.h",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         "@com_github_google_glog//:glog",
@@ -234,6 +249,7 @@
     name = "latency_lib",
     srcs = ["latency_lib.cc"],
     hdrs = ["latency_lib.h"],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         "//aos:realtime",
         "//aos/logging",
@@ -247,6 +263,7 @@
     srcs = [
         "signal_stress.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":latency_lib",
         "//aos:init",
@@ -260,6 +277,7 @@
     srcs = [
         "futex_latency.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":latency_lib",
         "//aos:condition",
@@ -274,6 +292,7 @@
     srcs = [
         "named_pipe_latency.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":latency_lib",
         "//aos:init",
@@ -287,6 +306,7 @@
     srcs = [
         "eventfd_latency.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     deps = [
         ":latency_lib",
         "//aos:init",
@@ -300,6 +320,7 @@
     srcs = [
         "print_lockless_queue_memory.cc",
     ],
+    target_compatible_with = ["@platforms//os:linux"],
     visibility = ["//visibility:public"],
     deps = [
         ":lockless_queue",