I've merged @rschulman's fixes to the test suite into my emscripten-new branch. Thanks @rschulman!
It sounds like there are still failing tests in stdtest, like those that spawn threads. These can similarly have
cfg_attr(target_os = "emscripten", ignore) attributes. @rschulman is going to look into those as well, but doesn't have a great deal of time this week.
--step check-target --target=asmjs-unknown-emscripten passes (with lots of ignored test cases if necessary) we can get PRs into rust-lang/rust. I'd like to do that by the end of this week, though friday/saturday is rustconf so it's going to be difficult.