[WebAssembly] Implement isCheapToSpeculateCtlz and isCheapToSpeculateCttz.

This unbreaks test/CodeGen/WebAssembly/i32.ll and
test/CodeGen/WebAssembly/i64.ll after r224899.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@253617 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed