[ASTWriter] Provide capability to output a PCM/PCH file that does not write...

[ASTWriter] Provide capability to output a PCM/PCH file that does not write out information about its output path

This is useful to enable sharing of the same PCH file even when it's intended for a different output path.

The only information this option disables writing is for `ORIGINAL_PCH_DIR` record which is treated as optional and (when present) used as fallback for resolving input file paths relative to it.

Differential Revision: https://reviews.llvm.org/D130710