If wxWidgets is linked to SDL, check what version it's actually linked
against instead of assuming it's linked to SDL1.2 (which isn't true on
Fedora 27).
* GTK3_API requires a wxWidget that support it too
=> avoid complexe compilation error
* SDL2_API requires a wxWidget without SDL support (wxUSE_LIBSDL = 0)
=> avoid run time crash
SDL check hypothesis: wx is linked against SDL1.2 and not SDL2. It would need to be improved on a distant future