[X86] Enable BT to be used in place of TEST for single bit checks under optsize

We already do this for 64-bit when it won't fit into a 64-bit AND/TEST's immediate field. This adds an additional qualifier to do it for any single bit constant larger than 8-bits under optsize

Differential Revision: https://reviews.llvm.org/D43346

llvm-svn: 325290