Parallelize singleton execution

Bug: 281536768
Test: manual, presubmits
Change-Id: I57fdc76ba6b277e88e196b506af87127a530fd37
diff --git a/cc/stub_library.go b/cc/stub_library.go
index f324dcc..3a6d0ae 100644
--- a/cc/stub_library.go
+++ b/cc/stub_library.go
@@ -23,7 +23,7 @@
 
 func init() {
 	// Use singleton type to gather all generated soong modules.
-	android.RegisterSingletonType("stublibraries", stubLibrariesSingleton)
+	android.RegisterParallelSingletonType("stublibraries", stubLibrariesSingleton)
 }
 
 type stubLibraries struct {