Add '-lstdc++' to the list of silently ignored libraries list that are always linked to default to hide the false warning about stdc++ library being missing.

emcc

@@ -840,7 +840,7 @@ try:
             break
         if found: break
       if found: break
-    if not found and lib not in ['GL', 'GLU', 'glut', 'm', 'SDL']: # whitelist our default libraries
+    if not found and lib not in ['GL', 'GLU', 'glut', 'm', 'SDL', 'stdc++']: # whitelist our default libraries
       logging.warning('emcc: cannot find library "%s"', lib)
 
   # If not compiling to JS, then we are compiling to an intermediate bitcode objects or library, so