[clang] [clang] [Driver] Fix respecting libdir when locating flang runtime (PR #127345)

[Michał Górny via cfe-commits]

mgorny wrote:

Sigh, looks like clang's driver is a mess around `lib`/`lib64` after all. So a proper solution would probably involve adding arch to the library name, and moving it into clang's resource directory.

https://github.com/llvm/llvm-project/pull/127345