[Basic] Don't rewrite source buffer copy multiple times

The on-disc buffer file name was not recorded correctly.

rdar://130478685

lib/AST/Module.cpp

@@ -907,7 +907,7 @@ ModuleDecl::getOriginalLocation(SourceLoc loc) const {
 
   SourceLoc startLoc = loc;
   unsigned startBufferID = bufferID;
-  while (std::optional<GeneratedSourceInfo> info =
+  while (const GeneratedSourceInfo *info =
              SM.getGeneratedSourceInfo(bufferID)) {
     switch (info->kind) {
 #define MACRO_ROLE(Name, Description)  \