lib/wasm: provide fs.constants.O_DIRECTORY definition

CL 606658 added a constants.Get("O_DIRECTORY").Int() call at init time,
which panics in browsers because O_DIRECTORY is undefined. It needs to
be a JavaScript number to avoid that.

Fixes #70723.

Change-Id: I727240bd25b47401d14a5e1a364d460708803f1f
Reviewed-on: https://go-review.googlesource.com/c/go/+/634455
TryBot-Bypass: Dmitri Shuralyov <[email protected]>
Auto-Submit: Dmitri Shuralyov <[email protected]>
Reviewed-by: Ian Lance Taylor <[email protected]>
Reviewed-by: Dmitri Shuralyov <[email protected]>
Reviewed-by: Zxilly Chou <[email protected]>

Author: dmitshur

lib/wasm/wasm_exec.js

@@ -14,7 +14,7 @@
 	if (!globalThis.fs) {
 		let outputBuf = "";
 		globalThis.fs = {
-			constants: { O_WRONLY: -1, O_RDWR: -1, O_CREAT: -1, O_TRUNC: -1, O_APPEND: -1, O_EXCL: -1 }, // unused
+			constants: { O_WRONLY: -1, O_RDWR: -1, O_CREAT: -1, O_TRUNC: -1, O_APPEND: -1, O_EXCL: -1, O_DIRECTORY: -1 }, // unused
 			writeSync(fd, buf) {
 				outputBuf += decoder.decode(buf);
 				const nl = outputBuf.lastIndexOf("\n");