Fix js library location in link.py (#23623)

This was broken when I move the library files in #23348

This was only used for generating the symbol lists, so the only side
effect was the the symbol lists would remain stale if somebody was
modifying the system libraries (i.e. it only effected emscripten
developers, not users).

Author: sbc100

tools/link.py

@@ -215,7 +215,8 @@ def get_js_sym_info():
   # and can contain full paths to temporary files.
   skip_settings = {'PRE_JS_FILES', 'POST_JS_FILES'}
   input_files = [json.dumps(settings.external_dict(skip_keys=skip_settings), sort_keys=True, indent=2)]
-  jslibs = glob.glob(utils.path_from_root('src') + '/library*.js')
+  jslibs = glob.glob(utils.path_from_root('src/lib') + '/lib*.js')
+  assert jslibs
   input_files.extend(read_file(jslib) for jslib in sorted(jslibs))
   for jslib in settings.JS_LIBRARIES:
     if not os.path.isabs(jslib):