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/genrule/genrule.go b/genrule/genrule.go
index 4dd2135..b9c2b10 100644
--- a/genrule/genrule.go
+++ b/genrule/genrule.go
@@ -248,7 +248,7 @@
 // Returns true if information was available from Bazel, false if bazel invocation still needs to occur.
 func (c *Module) GenerateBazelBuildActions(ctx android.ModuleContext, label string) bool {
 	bazelCtx := ctx.Config().BazelContext
-	filePaths, ok := bazelCtx.GetOutputFiles(label, ctx.Arch().ArchType)
+	filePaths, ok := bazelCtx.GetOutputFiles(label, android.GetConfigKey(ctx))
 	if ok {
 		var bazelOutputFiles android.Paths
 		exportIncludeDirs := map[string]bool{}