emulators/qemu-user-static: Fix build on recent FreeBSD

The swapoff(2) syscall recently changed from taking a single
argument to taking two (adding a field used for a "force" flag);
this broke qemu-user, since it translates system calls from
guest to host architecture.

Thanks to: imp
With hat: re@
Sponsored by: https://www.patreon.com/cperciva

(cherry picked from commit 688bd028652dc3c6bfe606fd690359060bbd949d)