misc/wasm: exit with code 1 if WebAssembly.instantiate fails

go_js_wasm_exec was returning with code 0 if WebAssembly.instantiate
failed. This made failing tests show as passed.

Change-Id: Icfb2f42e9f1c3c70ca4a130a61a63cb305edff32
Reviewed-on: https://go-review.googlesource.com/c/go/+/168885
Run-TryBot: Richard Musiol <neelance@gmail.com>
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Reviewed-by: Cherry Zhang <cherryyz@google.com>
TryBot-Result: Gobot Gobot <gobot@golang.org>

misc/wasm/wasm_exec.js

@@ -477,7 +477,7 @@
 		!global.process.versions.electron
 	) {
 		if (process.argv.length < 3) {
-			process.stderr.write("usage: go_js_wasm_exec [wasm binary] [arguments]\n");
+			console.error("usage: go_js_wasm_exec [wasm binary] [arguments]");
 			process.exit(1);
 		}
 
@@ -495,7 +495,8 @@
 			});
 			return go.run(result.instance);
 		}).catch((err) => {
-			throw err;
+			console.error(err);
+			process.exit(1);
 		});
 	}
 })();