FileNames: Support XDG paths handling under wxGTK 3.0

Signed-off-by: Mart Raudsepp <leio@gentoo.org>

src/AudacityApp.cpp

@@ -1049,7 +1049,9 @@ bool AudacityApp::OnInit() {
     wxFileSystem::AddHandler(safenew wxZipFSHandler);
 
     // encouraged by wxwidgets
+#if wxCHECK_VERSION(3, 1, 1)
     wxStandardPaths::Get().SetFileLayout(wxStandardPaths::FileLayout::FileLayout_XDG);
+#endif
 
     //
     // Paths: set search path and temp dir path

src/FileNames.cpp

@@ -47,6 +47,10 @@ used throughout Audacity into this one place.
 #include <windows.h>
 #endif
 
+#if defined(__WXGTK__) && !wxCHECK_VERSION(3, 1, 1)
+#include <glib.h>
+#endif
+
 static wxString gConfigDir;
 static wxString gDataDir;
 
@@ -246,6 +250,8 @@ FilePath FileNames::ConfigDir()
          // Use OS-provided user data dir folder
 #if defined(__WXMSW__)
          wxString configDir(wxStandardPaths::Get().GetUserConfigDir() + wxT("\\Tenacity"));
+#elif defined(__WXGTK__) && !wxCHECK_VERSION(3, 1, 1)
+         wxString configDir = wxString::Format(wxT("%s/tenacity"), g_get_user_config_dir());
 #else
          wxString configDir(wxStandardPaths::Get().GetUserConfigDir() + wxT("/tenacity"));
 #endif