[clang] [clang][driver] Use TheDriver.ClangExecutable in SetInstallDir to point to the actual install folder (PR #68091)

[Liviu Ionescu via cfe-commits]

ilg-ul wrote:

Another way to rephrase the question: the current implementation that preserves the symlinks, was it an explicitly required feature, or rather a side effect that came into existence by accident when implementing the current tests?

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