-void (*signal(int sig, void (*func)(int)))(int);
+typeof(void (int)) *signal(int sig, typeof(void (int)) *func);
-void (*signal(int sig, void (*func)(int)))(int);
+typeof(void (int)) *signal(int sig, typeof(void (int)) *func);
int(* fnptr_name)(int param) becomes typeof(int(int param))* fnptr_name
There is a recent proposal to update standard headers to this style: https://www.open-std.org/jtc1/sc22/wg14/www/docs/n3450.txt