Late evaluation of the fast-math vectorization requirement.

Late evaluation of the fast-math vectorization requirement.

This patch moves the verification of fast-math to just before vectorization is done. This way we can tell clang to append the command line options would that allow floating-point commutativity. Specifically those are enableing fast-math or specifying a loop hint.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@244489 91177308-0d34-0410-b5e6-96231b3b80d8