[SimplifyLibCalls] don't drop fast-math-flags on trig reflection folds (retry r339608)

Even though this code is below a function called optimizeFloatingPointLibCall(),
we apparently can't guarantee that we're dealing with FPMathOperators, so bail
out immediately if that's not true.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339618 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed