Use getTriple.isMIPS64() to detect 64-bit MIPS ABIs in
FreeBSD::getSupportedSanitizers() instead of getTriple.isMIPS32().
It would be nice to have a test for this regression.
AFAICT, I don't see a way to ask clang "which sanitizers are supported by this target". Hmm, the CHECK-SANL-MIPS test in tests/Driver/fsanitize.c seems like the closest match.