[ArgumentPromotion] Add a lit.local.cfg to disable X86 specific tests if the X86 target doesn't exist.

Hopefully this fixes some buildbot failure after r354376

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@354388 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed