Parallelize singleton execution

Bug: 281536768
Test: manual, presubmits
Change-Id: I57fdc76ba6b277e88e196b506af87127a530fd37
diff --git a/cc/cc.go b/cc/cc.go
index f4b5655..0e7f6c8 100644
--- a/cc/cc.go
+++ b/cc/cc.go
@@ -83,7 +83,7 @@
 		ctx.TopDown("sabi_deps", sabiDepsMutator)
 	})
 
-	ctx.RegisterSingletonType("kythe_extract_all", kytheExtractAllFactory)
+	ctx.RegisterParallelSingletonType("kythe_extract_all", kytheExtractAllFactory)
 }
 
 // Deps is a struct containing module names of dependencies, separated by the kind of dependency.