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
diff --git a/cc/object.go b/cc/object.go
index d8bb08f..43abb3a 100644
--- a/cc/object.go
+++ b/cc/object.go
@@ -54,7 +54,7 @@
 
 func (handler *objectBazelHandler) GenerateBazelBuildActions(ctx android.ModuleContext, label string) bool {
 	bazelCtx := ctx.Config().BazelContext
-	objPaths, ok := bazelCtx.GetOutputFiles(label, ctx.Arch().ArchType)
+	objPaths, ok := bazelCtx.GetOutputFiles(label, android.GetConfigKey(ctx))
 	if ok {
 		if len(objPaths) != 1 {
 			ctx.ModuleErrorf("expected exactly one object file for '%s', but got %s", label, objPaths)