Fix windows thread data issue and enhance windows os_mmap

[wenyongh]

Thread data should not be destroyed when thread exits, or other thread may not be able to join it. This PR saves the thread data into thread data list when thread exits, sets thread status and stores the return value, so that other thread can join it.

Also set MEM_TOP_DOWN flag for Windows VirtualAlloc to yield LLVM JIT relocation error. And set opt/size level to 3 for LLVM JIT for future use, currently the flags are not used by LLVM JIT.