Add a workaround to correctly align the stack before calling into C code.
When enough time has passed for users to update their userland the kernel
fix will be applied. This will change the ABI to have x0 point to the args
and sp be correctly aligned.

It is expected this compatibility code can be removed when the kernel and
qemu usermode emulation have both been updated for the new ABI.

This fixes clang failures, and most likely other crashes.

Obtained from: ABT Systems Ltd
Sponsored by: The FreeBSD Foundation