Check for comparisons of +/- zero when optimizing less-than-or-equal and

Check for comparisons of +/- zero when optimizing less-than-or-equal and
greater-than-or-equal SELECT_CCs to NEON vmin/vmax instructions.  This is
only allowed when UnsafeFPMath is set or when at least one of the operands
is known to be nonzero.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@97065 91177308-0d34-0410-b5e6-96231b3b80d8