configure: move GTK+ detection to Meson

This also allows removing CONFIG_NEED_X11, all the ingredients
can be computed easily in meson.build.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

configure

@@ -414,7 +414,7 @@ cfi="false"
 cfi_debug="false"
 seccomp="auto"
 glusterfs="auto"
-gtk="$default_feature"
+gtk="auto"
 tls_priority="NORMAL"
 gnutls="$default_feature"
 nettle="$default_feature"
@@ -1377,9 +1377,9 @@ for opt do
   --enable-uuid|--disable-uuid)
       echo "$0: $opt is obsolete, UUID support is always built" >&2
   ;;
-  --disable-gtk) gtk="no"
+  --disable-gtk) gtk="disabled"
   ;;
-  --enable-gtk) gtk="yes"
+  --enable-gtk) gtk="enabled"
   ;;
   --tls-priority=*) tls_priority="$optarg"
   ;;
@@ -2329,10 +2329,10 @@ if test "$cocoa" = "enabled"; then
     if test "$sdl" = "enabled"; then
         error_exit "Cocoa and SDL UIs cannot both be enabled at once"
     fi
-    if test "$gtk" = "yes"; then
+    if test "$gtk" = "enabled"; then
         error_exit "Cocoa and GTK UIs cannot both be enabled at once"
     fi
-    gtk=no
+    gtk=disabled
     sdl=disabled
 fi
 
@@ -2759,31 +2759,6 @@ EOF
   fi
 fi
 
-##########################################
-# GTK probe
-
-if test "$gtk" != "no"; then
-    gtkpackage="gtk+-3.0"
-    gtkx11package="gtk+-x11-3.0"
-    gtkversion="3.22.0"
-    if $pkg_config --exists "$gtkpackage >= $gtkversion"; then
-        gtk_cflags=$($pkg_config --cflags $gtkpackage)
-        gtk_libs=$($pkg_config --libs $gtkpackage)
-        gtk_version=$($pkg_config --modversion $gtkpackage)
-        if $pkg_config --exists "$gtkx11package >= $gtkversion"; then
-            need_x11=yes
-            gtk_cflags="$gtk_cflags $x11_cflags"
-            gtk_libs="$gtk_libs $x11_libs"
-        fi
-        gtk="yes"
-    elif test "$gtk" = "yes"; then
-        feature_not_found "gtk" "Install gtk3-devel"
-    else
-        gtk="no"
-    fi
-fi
-
-
 ##########################################
 # GNUTLS probe
 
@@ -3640,16 +3615,6 @@ EOF
   fi
 fi
 
-if test "$opengl" = "yes" && test "$have_x11" = "yes"; then
-  for target in $target_list; do
-    case $target in
-      lm32-softmmu) # milkymist-tmu2 requires X11 and OpenGL
-        need_x11=yes
-      ;;
-    esac
-  done
-fi
-
 ##########################################
 # libxml2 probe
 if test "$libxml2" != "no" ; then
@@ -5673,9 +5638,6 @@ fi
 if test "$module_upgrades" = "yes"; then
   echo "CONFIG_MODULE_UPGRADES=y" >> $config_host_mak
 fi
-if test "$need_x11" = "yes"; then
-  echo "CONFIG_NEED_X11=y" >> $config_host_mak
-fi
 if test "$pipe2" = "yes" ; then
   echo "CONFIG_PIPE2=y" >> $config_host_mak
 fi
@@ -5763,11 +5725,6 @@ fi
 if test "$bswap_h" = "yes" ; then
   echo "CONFIG_MACHINE_BSWAP_H=y" >> $config_host_mak
 fi
-if test "$gtk" = "yes" ; then
-  echo "CONFIG_GTK=y" >> $config_host_mak
-  echo "GTK_CFLAGS=$gtk_cflags" >> $config_host_mak
-  echo "GTK_LIBS=$gtk_libs" >> $config_host_mak
-fi
 if test "$gio" = "yes" ; then
     echo "CONFIG_GIO=y" >> $config_host_mak
     echo "GIO_CFLAGS=$gio_cflags" >> $config_host_mak
@@ -6501,7 +6458,7 @@ NINJA=$ninja $meson setup \
         -Dmalloc=$malloc -Dmalloc_trim=$malloc_trim -Dsparse=$sparse \
         -Dkvm=$kvm -Dhax=$hax -Dwhpx=$whpx -Dhvf=$hvf \
         -Dxen=$xen -Dxen_pci_passthrough=$xen_pci_passthrough -Dtcg=$tcg \
-        -Dcocoa=$cocoa -Dmpath=$mpath -Dsdl=$sdl -Dsdl_image=$sdl_image \
+        -Dcocoa=$cocoa -Dgtk=$gtk -Dmpath=$mpath -Dsdl=$sdl -Dsdl_image=$sdl_image \
         -Dvnc=$vnc -Dvnc_sasl=$vnc_sasl -Dvnc_jpeg=$vnc_jpeg -Dvnc_png=$vnc_png \
         -Dgettext=$gettext -Dxkbcommon=$xkbcommon -Du2f=$u2f -Dvirtiofsd=$virtiofsd \
         -Dcapstone=$capstone -Dslirp=$slirp -Dfdt=$fdt -Dbrlapi=$brlapi \