[X86] Model MXCSR for MMX FP instructions

Summary:
This patch models MXCSR and adds flag "mayRaiseFPException" for MMX FP
instructions.

Reviewers: craig.topper, andrew.w.kaylor, RKSimon, cameron.mcinally

Reviewed By: craig.topper

Subscribers: hiraditya, llvm-commits, LiuChen3

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D69702