CONFIGURE_ENV= ac_cv_path_GTK_ENCODE_SYMBOLIC_SVG="false"
adwaita-icon-theme is successor of gnome-icon-theme and gnome-icon-theme-symbolic,
and above trick will drop "gnome-icon-theme-symbolic" part,
and it is possible provide "adwaita-icon-theme-symbolic" sub package,
with TOOL_DEPENDS+gtk3+ and BUILD_DIRS= src/symbolic.
I keep changing my mind, and hoped that someone would explain The Right
Way in https://bugzilla.gnome.org/show_bug.cgi?id=741986 but apparently
not.
Say we split out -symbolic, as you suggest, then, as gedit (PR pkg/49494)
uses printer-symbolic, dialog-warning-symbolic, etc., we would end up
needing the dependency on the -symbolic part, so we might as well not
split adwaita, and just add to gedit the dependency on adwaita (as was
done for the PR).
Another way of looking at it is to split the package as you suggest,
and be content with gedit falling back to printer and dialog-warning
when -symbolic isn't found. So gedit would still be usable, but the
package wouldn't be quite right, unless one installed the -symbolic
part, which chances are one would do anyway.
Not much in it to decide...