[X86] Don't use fsin/fcos/fsincos instructions ever

Summary:
Previously we would use these instructions if sse was disabled and fastmath was enabled.

As mentioned in D28335, this is a bad idea.

Reviewers: efriedma, scanon, DavidKreitzer

Reviewed By: DavidKreitzer

Subscribers: zvi, llvm-commits

Differential Revision: https://reviews.llvm.org/D36344

llvm-svn: 310762