Generalize @llvm.ctlz, @llvm.cttz, and @llvm.ctpop to work on vectors of...

Generalize @llvm.ctlz, @llvm.cttz, and @llvm.ctpop to work on vectors of integers, and fix the one optimization pass that I'm aware of that needs updating for this.  At least one current target, ARM NEON, can implement these operations on vectors directly.

llvm-svn: 134265