Merge pull request #6052 from compnerd/ast-iwyu

Author: swift-ci

include/swift/AST/ModuleLoader.h

@@ -21,6 +21,7 @@
 #include "swift/Basic/LLVM.h"
 #include "swift/Basic/SourceLoc.h"
 #include "llvm/ADT/SetVector.h"
+#include "llvm/ADT/SmallSet.h"
 #include "llvm/ADT/TinyPtrVector.h"
 
 namespace swift {