[WiP] Try to fix Closure when building with -sENVIRONMENT=web

Details:
```
building:ERROR: Closure compiler run failed:

building:ERROR: /tmp/emscripten_temp_j4p9p4rt/vips-es6.jso3.js:5791:28: ERROR - [JSC_UNDEFINED_VARIABLE] variable process is undeclared
  5791| var wasmfsNodeIsWindows = !!process.platform.match(/^win/);
                                    ^^^^^^^

building:ERROR: /tmp/emscripten_temp_j4p9p4rt/vips-es6.jso3.js:6006:15: ERROR - [JSC_UNDEFINED_VARIABLE] variable require is undeclared
  6006| var nodePath = require("node:path");
                       ^^^^^^^

2 error(s), 0 warning(s)
```

Author: kleisauke

src/lib/libwasmfs_node.js

@@ -5,8 +5,28 @@
  */
 
 addToLibrary({
-  $wasmfsNodeIsWindows: "!!process.platform.match(/^win/)",
-  $nodePath: "require('node:path')",
+#if !ENVIRONMENT_MAY_BE_NODE
+  _wasmfs_node_readdir: (path_p, vec) => {},
+  _wasmfs_node_get_mode: (path_p, mode_p) => {},
+  _wasmfs_node_stat_size: (path_p, size_p) => {},
+  _wasmfs_node_fstat_size: (fd, size_p) => {},
+  _wasmfs_node_insert_file: (path_p, mode) => {},
+  _wasmfs_node_insert_directory: (path_p, mode) => {},
+  _wasmfs_node_unlink: (path_p) => {},
+  _wasmfs_node_rmdir: (path_p) => {},
+  _wasmfs_node_truncate: (path_p, len) => {},
+  _wasmfs_node_ftruncate: (fd, len) => {},
+  _wasmfs_node_open: (path_p, mode_p) => {},
+  _wasmfs_node_rename: (from_path_p, to_path_p) => {},
+  _wasmfs_node_symlink: (target_path_p, linkpath_path_p) => {},
+  _wasmfs_node_readlink: (path_p, target_p, bufsize) => {},
+  _wasmfs_node_close: (fd) => {},
+  _wasmfs_node_read: (fd, buf_p, len, pos, nread_p) => {},
+  _wasmfs_node_write: (fd, buf_p, len, pos, nwritten_p) => {},
+  _wasmfs_node_path_get_root: (path_p, target_p, bufsize) => {},
+#else
+  $wasmfsNodeIsWindows: "!!globalThis.process?.platform.match(/^win/)",
+  $nodePath: "ENVIRONMENT_IS_NODE ? require('node:path') : undefined",
 
   $wasmfsNodeConvertNodeCode__deps: ['$ERRNO_CODES'],
   $wasmfsNodeConvertNodeCode: (e) => {
@@ -194,7 +214,7 @@ addToLibrary({
     });
   },
 
-  _wasmfs_node_close__deps: [],
+  _wasmfs_node_close__deps: ['$wasmfsTry'],
   _wasmfs_node_close: (fd) => {
     return wasmfsTry(() => {
       fs.closeSync(fd);
@@ -228,5 +248,5 @@ addToLibrary({
   _wasmfs_node_path_get_root: (path_p, target_p, bufsize) => {
     return stringToUTF8(nodePath.parse(UTF8ToString(path_p)).root, target_p, bufsize);
   },
-
+#endif
 });

test/test_other.py

@@ -9292,6 +9292,31 @@ def test_noderawfs_open_abspath(self):
     ''')
     self.do_runf('open.c', cflags=['-sNODERAWFS'], args=[os.path.abspath('foo')])
 
+  def test_wasmfs_nodefs_stubs(self):
+    # This is essentially equivalent to building with `-sWASMFS -sNODERAWFS`, except that
+    # the Wasm binary can also be used on the web. Ensure that this use case is supported.
+    create_file('main.c', r'''
+      #include <emscripten/emscripten.h>
+      #include <emscripten/wasmfs.h>
+
+      EM_JS(bool, is_node, (), { return ENVIRONMENT_IS_NODE; });
+
+      backend_t wasmfs_create_root_dir() {
+          return is_node() ? wasmfs_create_node_backend("")
+                           : wasmfs_create_memory_backend();
+      }
+
+      backend_t wasmfs_create_working_dir(backend_t root_backend) {
+          return is_node() ? wasmfs_create_node_backend(".")
+                           : root_backend;
+      }
+
+      int main(int argc, char** argv) {
+        return 0;
+      }
+    ''')
+    self.run_process([EMCC, 'main.c', '-sWASMFS', '-sENVIRONMENT=web'])
+
   def test_noderawfs_readfile_prerun(self):
     create_file('foo', 'bar')
     self.add_pre_run("console.log(FS.readFile('foo', { encoding: 'utf8' }));")