dev-perl/Alien-wxWidgets: Fix use of wxwidgets eclass
EAPI5 auto-setup the wxwidgets magic, but EAPI6 requires explicit
invocation to function.
This omission means Alien-wxWidgets would get built with whatever was
currently selected with "eselect wxwidgets", ultimately resulting in
compilation failure in dev-perl/Wx when the wx implementation was
either wxGTK 2.8, or the GTK3 version of wxGTK3
Bug: https://bugs.gentoo.org/623042
Bug: https://bugs.gentoo.org/627180
Bug: https://bugs.gentoo.org/615246
Package-Manager: Portage-2.3.24, Repoman-2.3.6