[clang] [clang][driver] Use platform specific calls to get the executable absolute path (PR #68091)

[Liviu Ionescu via cfe-commits]

ilg-ul wrote:

> I haven't checked closely

Hi Martin, please check the #66704 bug report, the current behaviour is plainly wrong, clang does not pick the correct libraries and silently uses the system libraries, which leads to very subtle and hard to debug errors if the new version is several versions apart from the system.

I'm open to any suggestions to make clang correctly identify the InstalledDir when invoked via a symbolic link.
 

https://github.com/llvm/llvm-project/pull/68091