[PATCH][AArch64] Add llvm-mc test for asm code generated from all LLVM IR tests

[Tim Northover]

Hi Jiangning,

I think this might be a layering violation (I've CCed Jim Grosbach,
who's pretty much the authority). I know that object file tests are
discouraged from CodeGen, and this seems very similar.

I think the preferred option would be to make sure any test you
believe it's usefully doing is part of the test/MC hierarchy.

Cheers.

Tim.