With hardware boundary checking enabled, the app heap memory comes from `os_mmap()`.
Clearing the whole heap in the memory allocator causes process RSS to reach maximum
app heap size immediately and wastes lots of memory, so we had better remove the
unnecessary memory clean operations in the memory allocator.
1. Support cross building wamrc and installing it
2. Remove PIE flag for Windows to fix compilation error when compiled by clang
3. Support linking LLVM shared libs to help build with system default or custom
LLVM installation and reduce binary size.
If WASM app has called pthread_detach() to detach a thread, it will be detached again
when thread exits. Attempting to detach an already detached thread may result in crash
in musl-libc. This patch fixes it.
