I was hoping to say, let's drop SuSE 11.3, as SuSE 11.4 has glib version 2.28, which includes the function. Also ReadHat 5 drops support by the end of next month. But SLES still supports it until 2019.
As for the convenience method, I would not provide a compatibility header, as this would require additional checks and defines. Just hardcode the functionality in this case, although it seems to be a burden. An utility function which masks the compatibility could also be a possible solution. In extcap I came across this issue quite some time, and most of the time I ended up hardcoding the functionality.
regards
Roland