Add HSBuild project files and handle shared vs static use
Remove the multi-os-directory handling from the configure script

Does not interact nicely with the iOS toolchain.
Fix alignment of FFI_TYPE_FLOAT for Apple's ARM64 ABI
Fix non-variadic CIF initialization for Apple/ARM64

Turns out `aarch64_nfixedargs` wasn't initialized in the non-variadic
case, resulting in undefined behavior when allocating arguments.