[ValueTracking] Teach canCreateUndefOrPoison that ctpop does not create undef or poison.

This select of ctpop with 0 pattern can get left behind after
loop idiom recognize converts a loop to ctpop. LLVM 10 was able
to optimize this, but LLVM 11 and later is not. The difference
seems to be that some select transforms are now limited based
on canCreateUndefOrPoison.

Teaching canCreateUndefOrPoison about ctpop restores the
LLVM 10 codegen.

Differential Revision: https://reviews.llvm.org/D99207