[WebAssembly][NFC] Standardize SIMD multiclass format

Summary:
This CL changes the ExtractLane ISEL multiclass to more closely mirror
the structure of the splat and replace_lane multiclasses.

Reviewers: aheejin, dschuff

Subscribers: sbc100, jgravelle-google, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D50794

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@339801 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed