[FPEnv][X86] Constrained FCmp intrinsics enabling on X86

Summary: This is a follow up of D69281, it enables the X86 backend support for the FP comparision.

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

Subscribers: hiraditya, llvm-commits, annita.zhang, LuoYuanke, LiuChen3

Tags: #llvm

Differential Revision: https://reviews.llvm.org/D70582