[X86] Promote several single precision FP libcalls on Windows

A number of libcalls don't exist in any particular lib but are, instead,
defined in math.h as inline functions (even in C mode!).  Don't rely on
their existence when lowering @llvm.{cos,sin,floor,..}.f32, promote them
instead.

N.B. We had logic to handle FREM but were missing out on a number of
others.  This change generalizes the FREM handling.

llvm-svn: 268875