[X86][X86 intrinsics]Folding cmp(sub(a,b),0) into cmp(a,b) optimization

This patch adds new optimization (Folding cmp(sub(a,b),0) into cmp(a,b))
to instCombineCall pass and was written specific for X86 CMP intrinsics.

Differential Revision: https://reviews.llvm.org/D31398

llvm-svn: 300422