Some time ago, i use "GCC-M68k Binaries for Win95/NT" for
write some code to 68k cpus (not for amigaos). from readme:
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This zip file contains a version of GNU C/C++ which compiles for the Motorola 68k series of processors. The compiler is based on a copy of the Experimental GNU Compiler System(EGCS) V1.1.2 source code which is particularly suited to the building Win32 hosted ColdFire cross-compilers.
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in this pakage m68k-coff GNU assembler is it too. (i use this asm, and this work).
So, you can try create data file witch 68k instructions (without any file headers) and later write progs for adding
AmigaOs executable headers. But, in this case too - you can't use amiga libs, etc. but .. you can try create himself
and tool what can append amiga libs
btw, url :
http://sca.uwaterloo.ca/www.calm.hw.ac.uk/davidf/coldfire/download.htm