I tried mailing this to firstname.lastname@example.org but I never got an answer, so I'll try here. After inspecting the source code (only revdep-rebuild.sh and euse call gawk), I didn't see any obvious GNU extension being used. Maybe it could depends on virtual/awk instead (especially since this is the only stuff that `equery d gawk` gives).
*** Bug 652078 has been marked as a duplicate of this bug. ***
*** This bug has been marked as a duplicate of bug 652078 ***