Replacing HUGE_VALF with llvm::huge_valf in order to work around a warning triggered in MSVC 12.

Patch reviewed by Reid Kleckner and Jim Grosbach.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194533 91177308-0d34-0410-b5e6-96231b3b80d8