Clean up the deeply misleading name of the "MultiLibSuffix". This is
actually a MIPS-only hack to shim in random ABI directory suffixes in
numerous places throughout the toolchain's path search. It shouldn't
appear to be anything more general or useful.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@193595 91177308-0d34-0410-b5e6-96231b3b80d8