[WebAssembly] Convert MC tests to from bitcode to asm

Now that our `.s` format is stable(ish) and useable we should really
convert all our MC and lld tests over to .s format to match other
targets.

This is a test PR that just converts 2 of our MC tests to see what
it might look like.

Differential Revision: https://reviews.llvm.org/D71506