[clang][driver] accept maix32/maix64 gcc compat options

GCC on AIX primarily uses the -maix32 and -maix64 to select the bitmode
to target. In order to be compatible with existing build configurations,
clang should accept these options as well. In this patch we implement
these options for AIX targets.

Differential Revision: https://reviews.llvm.org/D145610