[WebAssembly][FastISel] Do not assume naive CmpInst lowering

Summary:
Fixes https://bugs.llvm.org/show_bug.cgi?id=40172. See
test/CodeGen/WebAssembly/PR40172.ll for an explanation.

Reviewers: dschuff, aheejin

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

Differential Revision: https://reviews.llvm.org/D56457

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@351127 91177308-0d34-0410-b5e6-96231b3b80d8
5 files changed