Fixed empty parameter list in signatures of internal functions.

src/haptic/darwin/SDL_syshaptic.c

@@ -189,7 +189,7 @@ SDL_SYS_HapticInit(void)
 }
 
 int
-SDL_SYS_NumHaptics()
+SDL_SYS_NumHaptics(void)
 {
     return numhaptics;
 }

src/haptic/linux/SDL_syshaptic.c

@@ -187,7 +187,7 @@ SDL_SYS_HapticInit(void)
 }
 
 int
-SDL_SYS_NumHaptics()
+SDL_SYS_NumHaptics(void)
 {
     return numhaptics;
 }

src/haptic/windows/SDL_windowshaptic.c

@@ -98,7 +98,7 @@ SDL_SYS_RemoveHapticDevice(SDL_hapticlist_item *prev, SDL_hapticlist_item *item)
 }
 
 int
-SDL_SYS_NumHaptics()
+SDL_SYS_NumHaptics(void)
 {
     return numhaptics;
 }