lib/gen-version-script.h: add getline and getdelim to notmuch.sym if needed

If the configure script detects missing getline and/or getdelim
symbols, then notmuch will use it's own versions. This patch, based on
id:"87k49v12i5.fsf@pc44es141.cs.uni-magdeburg.de" by Matthias
Guedemann, adds the symbols to notmuch.sym as well so they are
properly exported from the library.