Fix FTBFS with gcc 14

Signed-off-by: Michele Calgaro <michele.calgaro@yahoo.it>
(cherry picked from commit 447ba91ce6)

kalzium/src/solver/modwrap.c

@@ -21,8 +21,9 @@
 #include <stdio.h>
 #include <string.h>
 
-#include <caml/mlvalues.h>
+#include <caml/alloc.h>
 #include <caml/callback.h>
+#include <caml/mlvalues.h>
 
 char* solve_equation(const char * eq)
 {
@@ -32,6 +33,6 @@ char* solve_equation(const char * eq)
 		solve_equation_closure = caml_named_value("solve_equation");
 	}
 
-	return strdup(String_val(callback(*solve_equation_closure, copy_string(eq)) ));
+	return strdup(String_val(caml_callback(*solve_equation_closure, caml_copy_string(eq)) ));
 }