Parallelize singleton execution

Bug: 281536768
Test: manual, presubmits
Change-Id: I57fdc76ba6b277e88e196b506af87127a530fd37
diff --git a/android/module.go b/android/module.go
index db602a0..9024896 100644
--- a/android/module.go
+++ b/android/module.go
@@ -3724,7 +3724,7 @@
 }
 
 func init() {
-	RegisterSingletonType("buildtarget", BuildTargetSingleton)
+	RegisterParallelSingletonType("buildtarget", BuildTargetSingleton)
 }
 
 func BuildTargetSingleton() Singleton {