Remove the setjmp/longjmp stuff completely. Use signal

Remove the setjmp/longjmp stuff completely.  Use signal
handlers to set flags only (with exception for sigquit(),
which still seems to call some non-reentrant functions on
its way to _exit(2).)  That must eliminate the possibility
of catching SIGSEGV from following non-reentrant paths from
signal handlers.

PR:		bin/32740 bin/33846
Submitted by:	Maxim Konovalov <maxim@macomnet.ru>
Obtained from:	OpenBSD