Autoconf: sigh
wouter@country:~/nbd-2.9.11$ ./configure --host=m68k-linux --build=powerpc-linux [...] checking for m68k-linux-gcc... no checking for gcc... gcc [...] wouter@country:~/nbd-2.9.11$ ./configure --host=m68k-linux-gnu --build=powerpc-linux [...] checking for m68k-linux-gnu-gcc... m68k-linux-gnu-gcc [...]
So why do we have config.sub again?
config.sub is for any configure checks you want to do based on the triplet. You can just match the canonical triplet (or OS, or so forth).
You might have different toolchains for m68k-linux and m68k-linux-gnu, or for m68k-debian-linux and m68k-ubuntu-linux. So $target is honored when looking for tools.