Typo in gimpgradientselect.h include guard
I think the #ifndef
https://gitlab.gnome.org/GNOME/gimp/blob/master/libgimp/gimpgradientselect.h#L25
and the following #define
https://gitlab.gnome.org/GNOME/gimp/blob/master/libgimp/gimpgradientselect.h#L26
should match.
Trying to generate libgimp object introspection would fail because there are multiple identical definitions or something like that