[InstCombine] squash is-not-power-of-2 using ctpop

[InstCombine] squash is-not-power-of-2 using ctpop

This is the Demorgan'd 'not' of the pattern handled in:
D63660 / rL364153

This is another intermediate IR step towards solving PR42314:
https://bugs.llvm.org/show_bug.cgi?id=42314

We can test if a value is not a power-of-2 using ctpop(X) > 1,
so combining that with an is-zero check of the input is the
same as testing if not exactly 1 bit is set:

(X == 0) || (ctpop(X) u> 1) --> ctpop(X) != 1

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@364246 91177308-0d34-0410-b5e6-96231b3b80d8