[GlobalISel][X86] Prioritize Tablegen-erated instruction selection. NFC
[GlobalISel][X86] Prioritize Tablegen-erated instruction selection. NFC

Summary:
Prioritizes Tablegen-erated instruction selection over C++ instruction selection.
Remove G_ADD/G_SUB C++ selection - implemented by Tablegen.

Reviewers: dsanders, zvi, guyblank

Reviewed By: guyblank

Subscribers: rovka, llvm-commits, kristof.beyls

Differential Revision: https://reviews.llvm.org/D32677

git-svn-id: 0ff597fd157e6f4fc38580e8d64ab130330d2411@301792 91177308-0d34-0410-b5e6-96231b3b80d8

llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,apple/swift-llvm,apple/swift-llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,llvm-mirror/llvm,GPUOpen-Drivers/llvm,GPUOpen-Drivers/llvm,llvm-mirror/llvm,llvm-mirror/llvm