In 1.1.7 spellchecking (and gtkspell dependency) was made optional, however this is done in configure.in purely based on the presence of gtkspell without the possibility to explicitly state if it is wanted or unwanted.
There should be an enable type option for gtkspell, to be able to force it and not leave it up to automatic detection.

It would be nice if:
* when --enable-gtkspell is given to ./configure, configure bails if gtkspell is not found
* when --disable-gtkspell is given to ./configure, configure does not check for gtkspell at all, and spellchecking functionality is forced off
* when neither is passed, automatic detection is performed just like in 1.1.7

This kind of pattern is used in many projects, and is highly useful for a distribution such as Gentoo.

"gtkspell" could be "spellchecking" instead. I don't remember what suffix was used traditionally in GNOME apps, but I do think that tradition should be followed here :) Epiphany-2.16+ is one user of such a configure flag, f.ex