[WebAssembly] Update know failures for the wasm waterfall

Summary:
The waterfall no longer builds .s files and no longers uses
the wasm-o when it builds object files.

Subscribers: dschuff, jgravelle-google, aheejin, sunfish, llvm-commits

Differential Revision: https://reviews.llvm.org/D48371

llvm-svn: 335135