Disable nodejs warnings in test suite (#2973)
Disable nodejs warnings in test suite (#2973)

Fixes issue #2970

Avoids "Exception: 'run_command unexpected stderr'" when running wasm2js tests
with nodejs-14.5.0+, which is due to extra warnings from that node:

$ cd out/test/
$ /usr/bin/node --experimental-modules --loader /builddir/build/BUILD/binaryen-version_95/scripts/test/node-esm-loader.mjs a.2asm.mjs
(node:187299) ExperimentalWarning: --experimental-loader is an experimental feature. This feature could change at any time
(Use `node --trace-warnings ...` to show where the warning was created)

WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen,WebAssembly/binaryen