[X86] Rename CMPCCXADD intrinsics.

"__cmpccxadd_epi*" -> "_cmpccxadd_epi*"
This is to align with other intrinsics to follow single leading "_" style. Gcc
and intrinsic guide website will also apply this change.

Reviewed By: LuoYuanke, skan

Differential Revision: https://reviews.llvm.org/D140281