QFreeList object not freed on exit

This leak was introduced by 314c83c0c2f91532654f869b7dc6af1b7e8538da
Now in mutex.cpp with a compiler which don't support thread safe static variable, a function named freelist() is used to create the global QFreeList object,it will be created when the first time it was accessed, but will never be released. This will cause memory leak detector to report memory leaks.