Fix:

error: type specifier missing, defaults to 'int'; ISO C99 and later do not support implicit int [-Wimplicit-int]

https://github.com/cgdb/cgdb/issues/357
--- configure.orig	2022-01-16 09:43:35.000000000 -0600
+++ configure	2024-08-11 11:08:43.000000000 -0500
@@ -6512,7 +6512,7 @@
 #include <stdlib.h>
 #include <readline/readline.h>
 
-main()
+int main(void)
 {
 	FILE *fp;
 	fp = fopen("conftest.rlv", "w");