Modernize code

Can compile with arm-none-eabi-gcc 8.3.0
gbafix correctly handles ELF input

src/dma3_manager.c

@@ -8,7 +8,7 @@
 #define DMA_REQUEST_COPY16 3
 #define DMA_REQUEST_FILL16 4
 
-IWRAM_DATA struct
+BSS_DATA struct
 {
     const u8 *src;
     u8 *dest;