[X86] Use target independent masked expandload and compressstore intrinsics to...

[X86] Use target independent masked expandload and compressstore intrinsics to implement expandload/compressstore builtins.

Summary: We've had these target independent intrinsics for at least a year and a half. Looks like they do exactly what we need here and the backend already supports them.

Reviewers: RKSimon, delena, spatel, GBuella

Reviewed By: RKSimon

Subscribers: cfe-commits, llvm-commits

Differential Revision: https://reviews.llvm.org/D47693

llvm-svn: 334366