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/lottery.c

@@ -10,6 +10,9 @@
 #include <stdlib.h>
 #include "include/common.h"
 
+static void
+exit_cleanup(void);
+
 static void
 spew_buf(const void *data, size_t len);
 
@@ -22,6 +25,8 @@ main(int argc, char **argv)
 	(void) argc, (void) argv;
 	xpledgex("stdio", NULL);
 
+	(void) errhook(exit_cleanup);
+
 	buf = mkrbuf(BUFSIZ + 1);
 	if (!memcmp(buf, buf + (BUFSIZ >> 1), BUFSIZ >> 1))
 		same = 1;
@@ -73,3 +78,9 @@ spew_buf(const void *data, size_t len)
 
 	printf("%08zx\n", len);
 }
+
+static void
+exit_cleanup(void)
+{
+	return;
+}