Fix build with -Werror=incompatible-pointer-types that's due
to become a default on clang16.

https://bugs.gentoo.org/871162
--- a/src/exec.c
+++ b/src/exec.c
@@ -75,3 +75,3 @@
 	int	exitcode = -1;	/* initialize, to avoid warning */
-	const char	*argv[BUFSIZ];
+	char	*argv[BUFSIZ];
 	pid_t	p;