do not fail in test_dlfcn_qsort of js engine cannot do asm validation; fixes #1591

tests/test_core.py

@@ -5751,8 +5751,8 @@ def process(filename):
 
     if Settings.ASM_JS and os.path.exists(SPIDERMONKEY_ENGINE[0]):
       out = run_js('liblib.so', engine=SPIDERMONKEY_ENGINE, full_output=True, stderr=STDOUT)
-      assert 'asm' in out
-      self.validate_asmjs(out)
+      if 'asm' in out:
+        self.validate_asmjs(out)
 
   def test_dlfcn_data_and_fptr(self):
     if Settings.ASM_JS: return self.skip('this is not a valid case - libraries should not be able to access their parents globals willy nilly')