I'll probably make a exception for:
type complex.
Initialization of union/structs by member selection.
type long long.
Henk, even when I don't use your AHCC (yet), I'd like to ask you to consider also intermixed statements and declarations and '//' comments (if it isn't already implemented). These are the most important features I use from C99. (Just for the record, I've never used complex; 'long long' used maybe 2 times in my life).