Support for musl and alternative libc implementations in standad lib

[ghaith]

I ran into some issues building a static binary that links stdlib, so ended up going the musl route with musl.cc. Happy to work on integrating it further if it would be helpful.

Yes static linking stdlib is usually not possible, musl support would be nice indeed. We need to see how this fits in general, if we make it an option while building or leave it to the user. If we do leave it to the user, we will need to add the option in the build.sh file to allow for musl and compile the standard lib with musl as a target.

Discussion at #925

Originally posted by @ghaith in #867 (comment)