GTK: Update autotools config to use gtk3

This will depend on 3.24 as this is the only version I have available.
If someone else confirms it works on an older version we can lower it.

desmume/src/frontend/posix/configure.ac

@@ -138,7 +138,7 @@ dnl - Check for GTK and/or libglade
 FOUND_GLIB=no
 HAVE_ALSA=no
 GLIB_VER=2.8
-GTK_VER=2.14
+GTK_VER=3.24
 
 PKG_CHECK_MODULES(GLIB,
                   glib-2.0 >= $GLIB_VER,
@@ -146,7 +146,7 @@ PKG_CHECK_MODULES(GLIB,
                   FOUND_GLIB=no)
 
 PKG_CHECK_MODULES(GTK,
-                  gtk+-2.0 >= $GTK_VER,
+                  gtk+-3.0 >= $GTK_VER,
                   HAVE_GTK=yes,
                   HAVE_GTK=no)
 AC_SUBST(GTK_CFLAGS)

desmume/src/frontend/posix/gtk/meson.build

@@ -1,4 +1,4 @@
-dep_gtk3 = dependency('gtk+-3.0')
+dep_gtk3 = dependency('gtk+-3.0', version: '>=3.24')
 dep_x11 = dependency('x11')
 
 gtk_dependencies = dependencies + [dep_gtk3, dep_x11]