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

[Matheus Izvekov via cfe-commits]

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@@ -1458,6 +1458,20 @@ will be processed from the PCH file. Otherwise, Clang will report an error.
   ``test.h`` since ``test.h`` was included directly in the source file and not
   specified on the command line using ``-include-pch``.
 
+Ignoring a PCH File
+^^^^^^^^^^^^^^^^^^^
+
+To ignore a PCH file using Clang, the `-Xclang -ignore-pch` option is passed to
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mizvekov wrote:

I don't think we want to document frontend options in the User Manual, they are not supposed to be stable.

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