Newer GCC 4.5 and 4.6 do not produce a working binary

[jschwartzenberg]

As a user of Ubuntu 12.04, I have to explicitly install GCC 4.4 and use it to be able to compile syn68k correctly. With GCC 4.5 and 4.6 the test fails very quickly with:
syngentest: syn68k.c:671: : Assertion `emulation_depth >= 0' failed.

It would be great to findthe bug in either GCC or in syn68k.
In any case it would be useful to update the README for syn68k with info on known working GCC versions.