wimlib

The Clang also have full arm64 support, and it can be easily setup via MSYS2 without changing the configure script.

It's not something I've tried before. Traditionally MinGW was the only option, it seems this is new in the last 5 years or so. You're certainly welcome to try and report your results.

I have tried to build it, and it works well on MSYS2 environment. You don't need to change any code to support it.
You can consider using it to create ARM64 binaries.

Thanks. I've now made a number of improvements:

• Eliminated the dependencies on libxml2 and winpthreads, so wimlib is now easier to build for Windows.
• Added dllexport to the declarations in wimlib.h to avoid warnings when building for Windows with clang.
• Updated README.WINDOWS to show how to use MSYS2 (with the MINGW64, CLANG64, MINGW32, CLANG32, or CLANGARM64 environment). This replaces the previous instructions that used Cygwin and only had mingw64 and mingw32.
• Improved the tools/make-windows-release script.

That being said, I haven't yet actually tested CLANGARM64. It seems that build can only be done on a Windows ARM64 system.

ARM64 builds are now supported (but not yet actually tested!) using a prebuilt toolchain --- see viewtopic.php?p=1489#p1489.