ci: gentoo: use a slimmer base image

We've been using the desktop profile until now, mostly because it
automatically provides various frameworks we test e.g. wayland, gtk, qt
etc that all install out of the box. It also guarantees that binpackages
match.

The image is also really fat though. :( Switch to the base profile,
install a few packages that otherwise wouldn't be installed, and tweak
individual USE flags for binary coverage.

ci/ciimage/gentoo/image.json

@@ -1,5 +1,5 @@
 {
-  "base_image": "gentoo/stage3:desktop",
+  "base_image": "gentoo/stage3:latest",
   "env": {
     "CI": "1",
     "MESON_CI_JOBNAME": "linux-gentoo-gcc",

ci/ciimage/gentoo/install.sh

@@ -23,10 +23,16 @@ pkgs_stable=(
   dev-util/bindgen
 
   dev-libs/elfutils
+  dev-libs/protobuf
+
+  # modules
   dev-util/gdbus-codegen
+  dev-util/glib-utils
   dev-libs/gobject-introspection
   dev-util/itstool
-  dev-libs/protobuf
+  dev-util/wayland-scanner
+  dev-libs/wayland-protocols
+  dev-libs/wayland
 
   # custom deps
   dev-libs/boost
@@ -39,8 +45,12 @@ pkgs_stable=(
   dev-cpp/gtest
   sci-libs/hdf5
   dev-qt/linguist-tools
+  dev-qt/qtwidgets:5
   llvm-core/llvm
   dev-qt/qttools
+  net-print/cups
+  dev-util/vulkan-headers
+  media-libs/vulkan-loader
 
   # misc
   app-admin/sudo
@@ -60,9 +70,6 @@ pkgs_stable=(
   #dev-libs/wayland
   #dev-libs/wayland-protocols
   #dev-python/pypy3
-  #dev-qt/qtbase:6
-  #dev-qt/qtcore:5
-  #dev-qt/qttools:6
   #dev-vcs/mercurial
   #gnustep-base/gnustep-base
   #media-gfx/graphviz
@@ -100,10 +107,22 @@ mkdir /etc/portage/binrepos.conf || true
 mkdir /etc/portage/profile || true
 cat <<-EOF > /etc/portage/package.use/ci
 	dev-cpp/gtkmm X
+	media-libs/libglvnd X
+	x11-libs/cairo X
+	x11-libs/libxkbcommon X
 	dev-lang/rust clippy rustfmt
 	dev-lang/rust-bin clippy rustfmt
 	dev-libs/boost python
 
+	# slimmed binpkg, nomesa
+	media-libs/libsdl2 -opengl -wayland -alsa -dbus -gles2 -udev -vulkan
+	# binpkg
+	dev-qt/qtgui:5 dbus
+	dev-qt/qtwidgets:5 dbus gtk
+	media-libs/libsdl2 X
+	media-libs/vulkan-loader X
+	dev-libs/boost icu
+
 	# Some of these settings are needed just to get the binpkg but
 	# aren't negative to have anyway
 	sys-devel/gcc ada d