Forgot to mention that I was just trying to emerge gnome-light.
Managed to solve my problem by researching what dependencies are required by adwaita-icon-theme and found them in this link.
Apparently librsvg is required and was not present in my system so a simple emerge librsvg and then emerge x11-themes/adwaita-icon-theme was successful.
I also ran emerge gtk+ after emerge librsvg just to be sure that the gtk+ dependency was satisifed.
