I had selected the GTK3 of wxwidgets for my system with:
eselect wxwidgets list
Available wxWidgets profiles:
 gtk3-unicode-3.0-gtk3 *
and expected it to be selected in the compilation of mediainfo 19.09 too. I was surprised to see that this was not the case, however - the ebuild chose  over  above:
* Requested wxWidgets: 3.0
* Using wxWidgets: gtk2-unicode-3.0
This is due to this line in the ebuild:
Changing it to:
results in the right choice (for me):
* Requested wxWidgets: 3.0-gtk3
* Using wxWidgets: gtk3-unicode-3.0-gtk3
Note that with WX_GTK_VER="3.0", mediainfo will want to also install wxGTK in slot 3.0 - an extra, unnecessary step, given that I already have it in slot 3.0-gtk3.
But my point here is not to hardcode WX_GTK_VER to "3.0-gtk3", but to not hardcode it at all and honor the selection done by the user through 'eselect wxwidgets'.
(In reply to segmentation fault from comment #0)
> But my point here is not to hardcode WX_GTK_VER to "3.0-gtk3", but to not
> hardcode it at all and honor the selection done by the user through 'eselect
This is completely wrong. It is not possible to control build and runtime dependencies of ebuild via an external tool like eselect.
O.K. then, how should I go about it and let it choose gtk3-unicode-3.0-gtk3 over gtk2-unicode-3.0 when both are available in the system?
It's better to just switch to WX_GTK_VER="3.0-gtk3" if it works and there are no regressions.