[Driver] Support -muclibc / -mglibc command line options for a couple
of MIPS toolchains.

The uCLibc implemented for multiple architectures. A couple of MIPS toolchains
contains both uCLibc and glibc implementation so these options allow to select
used C library.

Initially -muclibc / -mglibc (as well as -mbionic) have been implemented in gcc
for various architectures so they are not MIPS specific.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@215552 91177308-0d34-0410-b5e6-96231b3b80d8