Here is the project,
http://code.google.ccom/p/libobjcgbarm
I wrote it out of my head, can contain bugs but compiles.
There's 6502 support some ARM7 support and a GameBoyAdvance toolkit in the works.
Includes libcarm, libc written with macros and objc. The whole project compiles with GNUstep makefiles.
Enjoy,
EH