Silence some error output in the presence of multi-step commands

[rickyvetter]

I am calling wasm-merge, wasm-metadce, and wasm-opt in sequence and the output of the first two steps both errors with "Some VMs may not accept this binary because it has a large number of locals in function". I think it makes sense to silence this error with some flag that implies that the result isn't final or that there are further optimizations that will be applied.

I'm not confident if this is the only type of error that it makes sense to do something like this and how special-cased the solution might be.

[kripken]

Does the --quiet flag not help there? If not then maybe we should make it apply to that. Another option might be -w to silence all warnings, perhaps, which I don't think we have yet. (I'm not sure which option is best.)

[rickyvetter]

This error isn't gated behind a --quiet check.

binaryen/src/wasm/wasm-binary.cpp

Line 477 in c8bfe28

std::cerr << "Some VMs may not accept this binary because it has a large "

I think either that or -w would be an improvement but maybe not ideal. My hesitancy with recommending either of those directly was around how this does feel like a context-dependent hard error. As a final artifact, this wasm file would be unusable and so in that context a --quiet silencing the error report would be a shame.