It appears that IAR just drops all linker options when converting from 4 to 5. Nice. Wonder why we other people prefer gcc and make 
I therefore split it up into EWARM4 and EWARM5 project directories. The LIB/EWARM5 linker file has an entry for the “branchtab” segment. Please test if that works. If it builds fine, but the DSO does not run, please send me your .map files.
EDIT: Fixed in commit 10633cf9