[WebAssembly] Update calls to computeKnownBits after the changes from r301620.

I didn't realize WebAssembly wasn't a default build target so I missed that changes were needed.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@301629 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed