add test case for argv[0] == null

test/unistd/exec-null.c

@@ -0,0 +1,13 @@
+/* make sure we handle argv[0] == NULL */
+
+#include <unistd.h>
+
+int main(int argc, char *argv[])
+{
+	if (argc == 0)
+		return 0;
+
+	char *exec_argv[1], *exec_envp[1];
+	exec_argv[0] = exec_envp[0] = NULL;
+	return execve("./exec-null", exec_argv, exec_envp);
+}