fixed clang warning

ecm.h.in

@@ -136,7 +136,7 @@ typedef __ecm_param_struct *ecm_params_ptr;
 #define ECM_MOD_REDC 4
 /* values <= -16 or >= 16 have a special meaning */
 
-const char *ecm_version();
+const char *ecm_version(void);
 int ecm_factor (mpz_t, mpz_t, double, ecm_params);
 void ecm_init (ecm_params);
 void ecm_reset (ecm_params);