[WebAssembly] Change SIMD lane indices to vec_i8imm_op

Summary: To explicitly opt out of LEB encoding for these immediates.

Reviewers: aheejin, dschuff

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

Differential Revision: https://reviews.llvm.org/D51766

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@341707 91177308-0d34-0410-b5e6-96231b3b80d8
1 file changed