Fix rts allocateExec() on NetBSD
Similar to SELinux, NetBSD "PaX mprotect" prohibits marking a page mapping both writable and executable at the same time. Use libffi which knows how to work around it.
Similar to SELinux, NetBSD "PaX mprotect" prohibits marking a page mapping both writable and executable at the same time. Use libffi which knows how to work around it.