Where to download the 4.5.0 ?
see it here:
http://amiga.sourceforge.net/phps/logger.php?download=GCC-4.5.0-m68k-amigaos-cygwin.7zbtw. its for cygwin, dunno if it works on some regular x86 linux, never tried. used it with amidevcpp package years ago..
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as an option, even though it sounds a bit far fetched, i think it should be possible to simply build aros68k toolchain, which contains 4.6.4 as default, there is also a patch for 6.x.x available, but it didnt always produce the right code, bigger binaries being a bit smaller in comparison. having amiga-m68k target installed it should likely be possible to compile with it a regular amiga program that doesnt depend on aros libs. resulting binary would be in elf format, but it can be converted to hunk with aros elf2hunk tool. voila! never tried it, but it should actually work.. i guess..