sigwaittest: Increase buffer to avoid overflow

Increase the size of the char buffer. gcc 9.1.1 reports:

src/sigwaittest/sigwaittest.c:494:5: note: ‘sprintf’ output between 5 and 14 bytes into a destination of size 8
  494 |     sprintf(f_opt, "-fr%d", i);
      |     ^~~~~~~~~~~~~~~~~~~~~~~~~~
src/sigwaittest/sigwaittest.c:522:24: warning: ‘%d’ directive writing between 1 and 10 bytes into a region of size 5 [-Wformat-overflow=]
  522 |     sprintf(f_opt, "-fs%d", i);
      |                        ^~

Signed-off-by: Daniel Wagner <wagi@monom.org>
Signed-off-by: John Kacur <jkacur@redhat.com>

src/sigwaittest/sigwaittest.c

@@ -352,7 +352,7 @@ int main(int argc, char *argv[])
 	struct params *sender = NULL;
 	sigset_t sigset;
 	void *param = NULL;
-	char f_opt[8];
+	char f_opt[14];
 	struct timespec launchdelay, maindelay;
 
 	process_options(argc, argv);