Merge pull request #39026 from apple/compnerd/39010

AST: repair the build after #39010

Author: shahmishal

include/swift/AST/USRGeneration.h

@@ -21,6 +21,8 @@
 
 #include "swift/Basic/LLVM.h"
 
+#include <string>
+
 namespace swift {
 class Decl;
 class AbstractStorageDecl;