gnatmake does not show up in YAST.
"make" does and may not be installed by default (I had to put it in myself on 10.3 and 11.0)
then put in "gcc" and "gcc-ada"
If you put in GPS, it has another version of gnatmake, but it is no longer needed, as the bugs it was built to fix have been covered by the standard install. (I *DO* like GPS, however, along with GIT-GUI)