Begin work in semi-standardized js_wasm32 target

core/runtime/os_specific_js.odin

@@ -0,0 +1,12 @@
+//+build js
+package runtime
+
+foreign import "odin_env"
+
+_os_write :: proc "contextless" (data: []byte) -> (int, _OS_Errno) {
+	foreign odin_env {
+		write :: proc "c" (fd: u32, p: []byte) ---
+	}
+	write(1, data)
+	return len(data), 0
+}