[clang] Insert headers in global module fragment (PR #151624)

[via cfe-commits]

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@@ -115,6 +134,7 @@ unsigned getOffsetAfterHeaderGuardsAndComments(StringRef FileName,
               return SM.getFileOffset(Tok.getLocation());
             return 0;
           }));
+  return std::max(HeaderAndPPOffset, ModuleDecl);
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JVApen wrote:

If rather say something like:
````
Determines the area where we want to insert header includes. This will be put (when available):
 - after `#pragma once`
 - in-between header guards (`#ifdef/#define` & `#endif`)
 - after opening global module (`module;`)
````
Feel free to rephrase or ignore

https://github.com/llvm/llvm-project/pull/151624