Avoid -Wstrict-prototypes diagnostics

Index: rts/include/stg/SMP.h
--- rts/include/stg/SMP.h.orig
+++ rts/include/stg/SMP.h
@@ -590,9 +590,9 @@ load_load_barrier(void) {
 EXTERN_INLINE void write_barrier(void);
 EXTERN_INLINE void store_load_barrier(void);
 EXTERN_INLINE void load_load_barrier(void);
-EXTERN_INLINE void write_barrier     () {} /* nothing */
-EXTERN_INLINE void store_load_barrier() {} /* nothing */
-EXTERN_INLINE void load_load_barrier () {} /* nothing */
+EXTERN_INLINE void write_barrier     (void) {} /* nothing */
+EXTERN_INLINE void store_load_barrier(void) {} /* nothing */
+EXTERN_INLINE void load_load_barrier (void) {} /* nothing */
 
 // Relaxed atomic operations
 #define RELAXED_LOAD(ptr) *ptr
