[driver][mips] Check both `gnuabi64` and `gnu` suffixes in `getMultiarchTriple`

In case of N64 ABI toolchain paths migth have `mips-linux-gnuabi64`
or `mips-linux-gnu` directory regardless of selected environment.
Check both variants while detecting a multiarch triple.

Fix for the bug https://bugs.llvm.org/show_bug.cgi?id=41204

llvm-svn: 357506