[clang] Make -frewrite-includes put an endif at the end of the included text (PR #67613)

[Erich Keane via cfe-commits]

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@@ -332,12 +346,14 @@ void InclusionRewriter::CommentOutDirective(Lexer &DirectiveLex,
     // OutputContentUpTo() would not output anything anyway.
     return;
   }
-  OS << "#if 0 /* expanded by -frewrite-includes */" << MainEOL;
+  OS << "#if 0 /* " << getIncludedFileName(Inc)
----------------
erichkeane wrote:

Hmm... ok.  The 'all or nothing' is fine.  As far as the system-includes, I wouldn't mind it if we were imperfect, as this is exclusively a debugging tool, thus any amount of ABI/API/etc stability doesn't really exist.  So I'm ok with a bit of a 'best effort' here (same on the enabling individual headers).  

we can always revise this as we determine needs.

BTW, I'm ok with this patch, but I am not the code owner here, so I'd like to give others a better chance to review this, particularly @MaskRay .

https://github.com/llvm/llvm-project/pull/67613