Make with the graphics.h included in all 3 source files that call functions from it.
MAX_TILES is defined in graphics.h
kamui@zetsuai:~/psp/dev/lieroPSP$ make
psp-gcc -I. -I/usr/local/pspdev/psp/sdk/include -G4 -Wall -O2 -L. -L/usr/local/pspdev/psp/sdk/lib main.o graphics.o mapEditor.o -losl -lpng -lz -lpspsdk -lpspctrl -lpspumd -lpsprtc -lpsppower -lpspgu -lpspaudiolib -lpspaudio -lm -lpspdebug -lpspdisplay -lpspge -lpspctrl -lpspsdk -lc -lpspnet -lpspnet_inet -lpspnet_apctl -lpspnet_resolver -lpsputility -lpspuser -lpspkernel -o lieroPSP.elf
graphics.o:(.sdata+0x0): multiple definition of `MAX_TILES'
main.o:(.sdata+0x0): first defined here
mapEditor.o:(.sdata+0x0): multiple definition of `MAX_TILES'
main.o:(.sdata+0x0): first defined here
collect2: ld returned 1 exit status
make: *** [lieroPSP.elf] Error 1
constant definition moved to main.c
kamui@zetsuai:~/psp/dev/lieroPSP$ make
psp-gcc -I. -I/usr/local/pspdev/psp/sdk/include -G4 -Wall -O2 -c -o main.o main.c
main.c: In function ‘main’:
main.c:16: warning: statement with no effect
psp-gcc -I. -I/usr/local/pspdev/psp/sdk/include -G4 -Wall -O2 -c -o graphics.o graphics.c
graphics.c: In function ‘loadTiles’:
graphics.c:10: error: ‘MAX_TILES’ undeclared (first use in this function)
graphics.c:10: error: (Each undeclared identifier is reported only once
graphics.c:10: error: for each function it appears in.)
graphics.c:11: warning: passing argument 1 of ‘oslLoadImageFile’ makes pointer from integer without a cast
make: *** [graphics.o] Error 1