[Driver] Select newest GCC installation on Solaris

As described in Issue #53709
<https://github.com/llvm/llvm-project/issues/53709>, since
28d58d8f
<https://reviews.llvm.org/rG28d58d8fe2094af6902dee7b4d68ec30a3e9d737>
`clang` doesn't find the latest of several parallel GCC installations on
Solaris, but only the first in directory order, which is pretty random.

This patch sorts GCC installations in reverse version order so the latest
is picked.

Tested on `sparcv9-sun-solaris2.11`, `amd64-pc-solaris2.11`, and
`x86_64-pc-linux-gnu`.

Differential Revision: https://reviews.llvm.org/D157275

(cherry picked from commit ae84ad15)