[test] Remove spidermonkey flag handling from config.py. NFC (emscripten-core#23737)

This flag is injected for testing purposes so is better places in
common.py along with other engine flags.

Author: sbc100

test/common.py

@@ -1187,6 +1187,7 @@ def setUp(self):
     self.ldflags = []
     # Increate stack trace limit to maximise usefulness of test failure reports
     self.node_args = ['--stack-trace-limit=50']
+    self.spidermonkey_args = ['-w']
 
     nodejs = self.get_nodejs()
     if nodejs:
@@ -1516,8 +1517,10 @@ def run_js(self, filename, engine=None, args=None,
       engine = self.js_engines[0]
     if engine == config.NODE_JS_TEST:
       engine = engine + self.node_args
-    if engine == config.V8_ENGINE:
+    elif engine == config.V8_ENGINE:
       engine = engine + self.v8_args
+    elif engine == config.SPIDERMONKEY_ENGINE:
+      engine = engine + self.spidermonkey_args
     try:
       jsrun.run_js(filename, engine, args,
                    stdout=stdout,

tools/config.py

@@ -63,12 +63,7 @@ def normalize_config_settings():
   if not JS_ENGINES:
     JS_ENGINES = [NODE_JS]
 
-  # Engine tweaks
-  if SPIDERMONKEY_ENGINE:
-    new_spidermonkey = SPIDERMONKEY_ENGINE
-    if '-w' not in str(new_spidermonkey):
-      new_spidermonkey += ['-w']
-    SPIDERMONKEY_ENGINE = fix_js_engine(SPIDERMONKEY_ENGINE, new_spidermonkey)
+  SPIDERMONKEY_ENGINE = fix_js_engine(SPIDERMONKEY_ENGINE, listify(SPIDERMONKEY_ENGINE))
   NODE_JS = fix_js_engine(NODE_JS, listify(NODE_JS))
   NODE_JS_TEST = fix_js_engine(NODE_JS_TEST, listify(NODE_JS_TEST))
   V8_ENGINE = fix_js_engine(V8_ENGINE, listify(V8_ENGINE))