[LoopIdiomRecognize] Add a test case showing that we transform to ctpop...

[LoopIdiomRecognize] Add a test case showing that we transform to ctpop without fully checking the 'x & (x-1)' part.

The code fails to check that the same value is used twice. We only make sure the left hand side of the and is part of the loop recurrence. The 'x' in the subtract can be any value.

llvm-svn: 331436