[mips][microMIPS] Mark symbols as microMIPS if necessary
Differential Revision: http://reviews.llvm.org/D6039
When run on a ppc64le based platform, the check-sanitizer build looks for
objects with the powerpc64le name. i.e. asan-powerpc64le.a
This change allows those objects to be built.

Differential Revision: http://reviews.llvm.org/D6043