[clang] [Driver] -include: deprecate probing .gch (PR #67084)

[Tom Honermann via cfe-commits]

tahonermann wrote:

I am also rather uncomfortable with this behavioral change. There are a lot of build systems in use out there. My preference would be to continue to probe for a .gch file, but also validate that it is a (compatible) Clang PCH file before trying to use it.

https://github.com/llvm/llvm-project/pull/67084