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

[Matheus Izvekov via cfe-commits]

================
@@ -31,6 +31,16 @@ option:
 
   $ clang -cc1 -include-pch test.h.pch test.c -o test.s
 
+To ignore PCH options, use the option `-ignore-pch`:
+
+.. code-block:: bash
+
+  $ clang -cc1 test.h -emit-pch -ignore-pch -o test.h.pch
+  $ clang -cc1 -include-pch test.h.pch -ignore-pch test.c -o test.s
+
+This option disables precompiled headers, overrides -emit-pch and -include-pch.
+test.h.pch is not generated and not used as a prefix header.
+
----------------
mizvekov wrote:

Since there is no frontend option, this shouldn't be added.
```suggestion
```

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