clock_time_get defaults to Date.now() rather than performance.now()

[curiousdannii]

The WASI function clock_time_get is meant to return nanosecond precision, but Emscripten's implementation uses Date.now() in realtime mode rather than performance.now(). The latter can at best only do microsecond precision, but that's much better than the former's millisecond precision. (Browsers will typically restrict it to 100 microsec precision, but that's still 10 times better than Date.now(). Node should get the full microsec detail.)

I'm sure there are lots of tricky edge cases here which I don't know about, but this seems like it should be broadly possible?

emscripten/src/lib/libwasi.js

Lines 164 to 167 in 7080730

	if (clk_id === {{{ cDefs.__WASI_CLOCKID_REALTIME }}}) {
	now = _emscripten_date_now();
	} else if (nowIsMonotonic) {
	now = _emscripten_get_now();

Something like this?

if (clk_id === {{{ cDefs.__WASI_CLOCKID_REALTIME }}}) {
      now = performance.timeOrigin + _emscripten_get_now();
}