From the license information site of wxWidgets it seems that they use a simple LGPL 2 or later with an exception stating that derived works in binary form may be distributed on the user's own terms.
That exception can be stripped away by any contributor, so since Gentoo applies some patches, the wxGTK version in Gentoo can be made either LGPL or wxWinLL-3 by setting the license of the patches as either LGPL or wxWinLL-3.
Why I write that: I just checked which of my installed programs are NOT under FSF-APPROVED licenses and wxGTK was the only one. Since wxGTK could be made LGPL by the patches, I could then set ACCEPT_LICENSE to "@FSF-APPROVED".
1. As a special exception, the copyright holders of this library give
permission for additional uses of the text contained in this release of
the library as licenced under the wxWindows Library Licence, applying
either version 3.1 of the Licence, or (at your option) any later version of
the Licence as published by the copyright holders of version
3.1 of the Licence document.
2. The exception is that you may use, copy, link, modify and distribute
under your own terms, binary object code versions of works based
on the Library.
3. If you copy code from files distributed under the terms of the GNU
General Public Licence or the GNU Library General Public Licence into a
copy of this library, as this licence permits, the exception does not
apply to the code that you add in this way. To avoid misleading anyone as
to the status of such modified files, you must delete this exception
notice from such code and/or adjust the licensing conditions notice
4. If you write modifications of your own for this library, it is your
choice whether to permit this exception to apply to your modifications.
If you do not wish that, you must delete the exception notice from such
code and/or adjust the licensing conditions notice accordingly.
wxWinLL-3 is basically (L)GPL-2 with a special exemption that you can distribute binaries (modified or not) under your own terms (point 2). This doesn't apply here since we don't distribute any binaries. I don't think point 4 applies either as all our modifications/patches are GPL-2 which means we fall under point 3, which just says that any GPL-2 code added to the library doesn't qualify for the exception.
There's nothing that says making GPL-2 licensed modifications changes the license of the library, just that you can distribute binaries under your own terms. We don't, so we can't.
As I understand point point 4, it says that you can choose whether you want the exception to apply to your own code.
And since your patches are GPL without exception, the whole work can only be put under the GPL - which automatically strips away the exception for the whole work.
So the binaries produced when using GPL/LGPL patches (the "entire product") are automatically LGPL/GPL without exception, as long as the patch author doesn't carry over the exception into his/her contribution.
What doesn't change is the license of the code, but the license of the "entire work" has to fit every single part, so adding GPL-2 patches makes the entire work GPL-2.
(If I had found license notices in the patches, I'd have written that directly)
But what LICENSE reflects is the license of the code as we distribute it, not the binaries that are created through the compilation process, which, i agree, could be considered LGPL or whatever license you choose to distribute them as under the exception.
Furthermore, from a non-technical viewpoint, the license of wxWidgets is explicitly designed to allow the possibility of distributing the wx libraries under licenses that are less permissive than the LGPL, so that distributors are not obliged to distribute the source with the binaries. So I don't believe that this holds with what @FSF-APPROVED is supposed to represent. In the end I'd rather accurately and impartially describe the state of the code than strip away upstream's intentions to make it fit in a license group.