[X86] Add a memory clobber to the bittest intrinsic inline asm. Get default clobbers from the target
I believe the inline asm emitted here should have a memory clobber since it writes to memory.
It was also missing the dirflag clobber that we use by default along with flags and fpsr. To avoid missing defaults in the future, get the default list from the target
Differential Revision: https://reviews.llvm.org/D88121