Get test suite working with wasm

[brson]

Last I looked compiletest could not deal with wasm as outputted today by rustc because the binaryen interpreter expects the wasm file to be located in a specific relative path that compiletest does not set up correctly.

I recall the fix being a matter of refactoring compiletest to pass certain paths down to the process spawning node.

[brson]

This is still a critical wasm bug, and not a difficult one to fix. Run the test suite against the wasm target to see how it's currently broken. Most should simply be failing to load the wasm correctly. It should be possible to get verbose output from the test suite, then take that output and run the node.js test command by hand to figure out the correct invocation; then modify compiletest to do it correctly.

[richard-uk1]

I'm going to have a look at this but I make no promises so someone else who wants to take it should do so.

[richard-uk1]

OK my strategy is

1. Make compiletest::procsrv::run and compiletest::procsrv::run_background take an extra parameter, current_dir: Option<String>, and if Some add cmd.current_dir to command.
2. Pass None to these functions everywhere that calls them
3. For emscripten, set it to Some(self.output_base_name().parent()) in compiletest::runtest::program_output

I'm away for a few days so if this looks good I'll probably do it on wednesday :)

[richard-uk1]

Oh and I also had to pass "-s BINARYEN_METHOD='native-wasm,interpret-binary'" as it defaulted to just native-wasm, which I think isn't implemented yet (I'm still trying to understand emscripten properly).

[alexcrichton]

I believe this has largely be done and can be verified with the containers in-tree, so closing.