[Modules] Include the header needed for make_unique, otherwise we can't

build this header in a module.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@231561 91177308-0d34-0410-b5e6-96231b3b80d8

include/llvm/IR/PassManagerInternal.h

@@ -19,6 +19,7 @@
 #define LLVM_IR_PASSMANAGERINTERNAL_H
 
 #include "llvm/ADT/StringRef.h"
+#include "llvm/ADT/STLExtras.h"
 
 namespace llvm {