Clean up Closure warnings when targeting WASM2JS.

[juj]

This enables Closure spam free wasm2js test suite runs.

Even though the checkTypes annotation doesn't do anything in wasm2js.js file for WebAssembly, I'm still adding it there because otherwise in six months me or someone else would look at that Closure warning and have a first impression "oh, that's just missing a checkTypes suppress."

Muting these warnings globally in Closure for WASM2JS runs isn't that bad, since any developer who is targeting WASM2JS will also very likely target regular Wasm runs, and there they will see any checkTypes/uselessCode related diagnostics, giving them the needed coverage.

[kripken]

Perhaps add a test confirming no warnings remain, somewhere?

[juj]

Perhaps add a test confirming no warnings remain, somewhere?

Closure prints its warnings in all caps WARNING - .... In my CI setup I use that to highlight the run results in orange, which is how I noticed this. So in that perspective we do have coverage.

(I presume we'd have to run all tests to ensure they really don't warn? so that would be a test to run all tests..)

[kripken]

Well, I just mean a single test, for basic coverage. E.g. like this existing test:

  @with_env_modify({'EMCC_LOGGING': '0'})  # this test assumes no emcc output
  def test_no_warnings(self):
    # build once before to make sure system libs etc. exist
    self.run_process([EMXX, test_file('hello_libcxx.cpp')])
    # check that there is nothing in stderr for a regular compile
    err = self.run_process([EMXX, test_file('hello_libcxx.cpp')], stderr=PIPE).stderr
    self.assertEqual(err, '')

But maybe it's not worth it, lgtm either way.

[juj]

But maybe it's not worth it, lgtm either way.

Hmm, I think probably better to work towards running the test suite with -Werror=closure altogether, so that all compilation with Closure would check against warnings.

[sbc100]

We already run with -Werror by default which applies to closure warnings. So as long as a test using the default flags we already cover this case, so I don't think we should need any special testing.

[sbc100]

I think there are a bunch of tests that have -Wno-closure to avoid these issues.

Those should be removed as part of this PR, right?

[sbc100]

Does closure compile run on the generated wasm2js output code? I guess it must otherwise this would not be needed.

[juj]

Yeah it does, I think this is because the WASM2JS output is so huge that it needs Closure to help make it half-reasonable.

[juj]

I think there are a bunch of tests that have -Wno-closure to avoid these issues.

Those should be removed as part of this PR, right?

Indeed, looks like these aren't needed anymore. Removed.