Re-enabling MCJIT tests on ARM

After several refactorings on the MCJIT remote communication, things are
finally looking good on Clang-compiled LLVM regarding MCJIT remote tests,
so I'm re-enabling them to see how the self-hosting buildbot behaves over
a longer period.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@200102 91177308-0d34-0410-b5e6-96231b3b80d8