[clang] [Frontend][PCH]-Add support for ignoring PCH options (-ignore-pch). (PR #142409)

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@@ -31,6 +31,16 @@ option:
 
   $ clang -cc1 -include-pch test.h.pch test.c -o test.s
 
+To ignore PCH options using ``clang -cc1``, use the option `-ignore-pch`:
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MaggieYingYi wrote:

Thanks again for explaining the document rule.

> Nonetheless, I think `-ignore-pch` doesn't make sense as a frontend flag, only as a driver flag.

I will update `-ignore-pch` as a driver option which is similar as the `-include-pch` option. Once `-ignore-pch` is a driver option, it needs to be documented on the UserManual. 


https://github.com/llvm/llvm-project/pull/142409