Solved a bunch of -Wall errors on modern

src/link_rfu_2.c

@@ -699,8 +699,7 @@ void StopUnionRoomLinkManager(void)
     gRfu.state = RFUSTATE_UR_STOP_MANAGER;
 }
 
-// Unused
-static void ReadySendDataForSlots(u8 slots)
+static void UNUSED ReadySendDataForSlots(u8 slots)
 {
     u8 i;
 
@@ -2146,7 +2145,7 @@ void RfuSetErrorParams(u32 errorInfo)
     }
 }
 
-static void ResetErrorState(void)
+static void UNUSED ResetErrorState(void)
 {
     gRfu.errorState = RFU_ERROR_STATE_NONE;
 }
@@ -2560,8 +2559,7 @@ static void VBlank_RfuIdle(void)
     TransferPlttBuffer();
 }
 
-// Unused
-static void Debug_RfuIdle(void)
+static void UNUSED Debug_RfuIdle(void)
 {
     s32 i;
 
@@ -2934,7 +2932,7 @@ static void Debug_PrintEmpty(void)
         Debug_PrintString(sASCII_30Spaces, 0, i);
 }
 
-static void Debug_PrintStatus(void)
+static void UNUSED Debug_PrintStatus(void)
 {
     s32 i, j;
     Debug_PrintNum(GetBlockReceivedStatus(), 28, 19, 2);
@@ -2990,7 +2988,7 @@ static void Debug_PrintStatus(void)
     }
 }
 
-static u32 GetRfuSendQueueLength(void)
+static u32 UNUSED GetRfuSendQueueLength(void)
 {
     return gRfu.sendQueue.count;
 }