[Driver] Unsupport --print-multiarch

* If GCC is configured with `--disable-multi-arch`, `--print-multiarch` output is an empty line.
* If GCC is configured with `--enable-multi-arch`, `--print-multiarch` output may be a normalized triple or (on Debian, 'vendor' is omitted) `x86_64-linux-gnu`.

The Clang support D101400 just prints the Debian multiarch style triple
unconditionally, but the string is not really expected for non-Debian systems.

AIUI many Linux distributions and non-Linux OSes don't configure GCC with `--enable-multi-arch`.
Instead of getting us in the trouble of supporting all kinds of variants, drop the support as before D101400.

Close https://github.com/llvm/llvm-project/issues/51469

Reviewed By: phosek

Differential Revision: https://reviews.llvm.org/D133170