bhyveload: Factor global variables into a software context

[markj]

Summary

This will make it easier to port bhyveload's functionality into the main
bhyve executable.

No functional change intended.

[wanpengqian_gmail.com]

usr.sbin/bhyveload/bhyveload.c

594

This restores sc->term, but main() has already run cfmakeraw() on it. The old code kept a separate oldterm, so this now restores the raw settings, and the terminal is left in raw mode when bhyveload exits.

[wanpengqian_gmail.com]

usr.sbin/bhyveload/bhyveload.c

996–998

loader_hdl is now a non-volatile local that is assigned after setjmp(), so its value is indeterminate here after longjmp(). The swap-interpreter and reboot paths may dlclose() garbage.

[markj]

Address review comments

[novel]

usr.sbin/bhyveload/bhyveload.c

872

should it be void * volatile instead, i.e. volatile pointer rather than pointer to volatile data as it is now?

[markj]

Fix the qualifier on loader_hdl.