[X86][FPEnv] Promote some float strictfp operations to double on...

[X86][FPEnv] Promote some float strictfp operations to double on i686-pc-windows-msvc to match what we do for non-strict.

The float libcalls are inlined in MSVC's math header where they
just cast to double and use the double libcall. Do the same when
we emit libcalls.