mips64-expansions.s fails on ARM and x86-64 (Linux)

With ToT on ARM and x86-64 Linux I see:

******************** TEST 'LLVM :: MC/Mips/mips64-expansions.s' FAILED


I see the failure in the builders but ToT is working for me on x86_64 Linux. According to the ppc64 builder it started failing after r224675-r224677 (http://lab.llvm.org:8011/builders/clang-ppc64-elf-linux2/builds/16860, the previous build failed for different reasons). These three commits are all David Majnemer's but his commits don't sound related to the failures.

This is probably pr22006. Looking at it.