cmdline: allow overriding -jsD directives (#26576)

Author: subhaushsingh

test/test_jslib.py

@@ -356,6 +356,8 @@ def test_jslib_custom_settings(self):
     self.cflags += ['--js-library', test_file('jslib/test_jslib_custom_settings.js'), '-jsDCUSTOM_JS_OPTION=1']
     self.do_run_in_out_file_test('jslib/test_jslib_custom_settings.c')
 
+    self.run_process([EMCC, test_file('hello_world.c'), '-jsDCUSTOM_JS_OPTION=1', '-jsDCUSTOM_JS_OPTION=2'])
+
     self.assert_fail([EMCC, '-jsDWASM=0'], 'cannot change built-in settings values with a -jsD directive')
 
   def test_jslib_native_deps(self):

tools/cmdline.py

@@ -216,6 +216,7 @@ def parse_args(newargs):  # noqa: C901, PLR0912, PLR0915
   """
   should_exit = False
   skip = False
+  user_js_defines = set()
   LEGACY_ARGS = {'--js-opts', '--llvm-opts', '--llvm-lto', '--memory-init-file'}
   LEGACY_FLAGS = {'--separate-asm', '--jcache', '--proxy-to-worker', '--default-obj-ext',
                   '--embind-emit-tsd', '--remove-duplicates', '--no-heap-copy'}
@@ -575,8 +576,9 @@ def consume_arg_file():
         key, value = key.split('=')
       else:
         value = '1'
-      if key in settings.keys():
+      if key in settings.keys() and key not in user_js_defines:
         exit_with_error(f'{arg}: cannot change built-in settings values with a -jsD directive. Pass -s{key}={value} instead!')
+      user_js_defines.add(key)
       # Apply user -jsD settings
       settings[key] = value
       newargs[i] = ''