Add OS to configuration key in mixed builds

This also removes the special-case filegroup from mixed builds
buildroot; no special handling is required. Since we're currently
hardcoding linux_x86_64 as our host platform, it should be fine
to continue assumping that hardcoded host for now.

Test: USE_BAZEL_ANALYSIS=1 m adbd
Change-Id: I35509f4eb33ba7a243fab4c34b35958f6f2fceab

cc/prebuilt.go

@@ -330,7 +330,7 @@ type prebuiltStaticLibraryBazelHandler struct {
 
 func (h *prebuiltStaticLibraryBazelHandler) GenerateBazelBuildActions(ctx android.ModuleContext, label string) bool {
 	bazelCtx := ctx.Config().BazelContext
-	ccInfo, ok, err := bazelCtx.GetCcInfo(label, ctx.Arch().ArchType)
+	ccInfo, ok, err := bazelCtx.GetCcInfo(label, android.GetConfigKey(ctx))
 	if err != nil {
 		ctx.ModuleErrorf("Error getting Bazel CcInfo: %s", err)
 	}