Can't you compile with the -xc99 option? The Sun documentation says it's supported, even with that old compiler:
http://developers.sun.com/sunstudio/support/Ccompare.html#upd2e 'configure' should have deduced the -xc99 option for you; it tries '-xc99=all' early on. Does that not work for you? The documentation says '-xc99=%all' is required, but as I recall, the '%' was optional even way back when. Perhaps you can send in a copy of your 'configure' command, and the resulting 'config.log' file?
