If 2.5 ulp is acceptable, denormals are not required, and
isn't a reciprocal which will already be handled, replace
with a faster fdiv.
Simplify the lowering tests by using per function
subtarget features.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@276051 91177308-0d34-0410-b5e6-96231b3b80d8