libreboot-utils: unified error handling

i now use a singleton hook function per program:
nvmutil, mkhtemp and lottery

call this at the startup of your program:

(void) errhook(exit_cleanup);

then provide that function. make it static,
so that each program has its own version.

if you're writing a program that handles lots
of files for example, and you want to do certain
cleanup on exit (including error exit), this can
be quite useful.

Signed-off-by: Leah Rowe <leah@libreboot.org>

util/libreboot-utils/lib/num.c

@@ -51,6 +51,6 @@ void
 check_bin(size_t a, const char *a_name)
 {
 	if (a > 1)
-		err_no_cleanup(0, EINVAL, "%s must be 0 or 1, but is %lu",
+		err_exit(EINVAL, "%s must be 0 or 1, but is %lu",
 		    a_name, (size_t)a);
 }