[InstCombine] In foldSelectICmpAnd, if we need to to truncate from the 'and'...

[InstCombine] In foldSelectICmpAnd, if we need to to truncate from the 'and' type to the 'select' type, do it after shifting right instead of just bailing.

Previously we were always trying to emit the zext or truncate before any shift. This meant if the 'and' mask was larger than the size of the truncate we would skip the transformation.

Now we shift the result of the and right first leaving the bit within the range of the truncate.

This matches what we are doing in foldSelectICmpAndOr for the same problem.

llvm-svn: 310159