Have you checked out bebbo's cross-platform GCC 6.x 68K port? Even has initial stages of remote debugging! Tony Wilen's PFS is now compiled with this system (for example) with the resulting binaries smaller than previous versions. Bebbo has spent quite some time on getting the optimizations to a good point.
More info here:
http://eab.abime.net/forumdisplay.php?f=118And his github page:
https://github.com/bebbo/amiga-gcc
