[clang] [flang] [driver] Generalize the code that adds the path of libflang_rt.runtime.a. (PR #134362)

[Michał Górny via cfe-commits]

mgorny wrote:

> I find this change quite confusing. It seems that `-static-libflangrt` now expects entirely different install location than `-shared-libflangrt`.

Ah, sorry, now I see that `-L/usr/lib/llvm/21/bin/../../../../lib/clang/21/lib/x86_64-pc-linux-gnu` is also added, so the "resource dir" location should work for both options.

https://github.com/llvm/llvm-project/pull/134362