github-actions: Improve cppcheck accuracy

Give it relevant -D/-I flags so it can perform more useful checks.
This makes if slower, but hopefully more accurate and useful.

.github/workflows/build.yml

@@ -231,5 +231,35 @@ jobs:
           sudo apt-get install --assume-yes --no-install-recommends \
             cppcheck ${DEB_LIBRARY_DEPS} ${DEB_LIBRARY_DEPS_MATE_DESKTOP}
 
+      # - ignore non-source directories
+      # - define relevant configuration I can think of
+      #   - X11-related stuff
+      #   - Wayland-related stuff
+      #   - in-process for Wayland
+      #   - optional features
+      # - -I flags from pkg-config (grepped from configure.ac)
       - name: cppcheck
-        run: cppcheck --enable=warning,style,performance,portability,information,missingInclude -i'gtk-layer-shell-build' .
+        env:
+          checks: warning,style,performance,portability,information,missingInclude
+          defines: >
+            -DHAVE_X11 -DHAVE_RANDR
+            -DHAVE_WAYLAND
+            -DCLOCK_INPROCESS -DFISH_INPROCESS -DNOTIFICATION_AREA_INPROCESS -DWNCKLET_INPROCESS
+            -DHAVE_WINDOW_PREVIEWS
+          packages: >
+            gdk-pixbuf-2.0
+            gio-unix-2.0
+            gmodule-2.0
+            gtk+-3.0
+            ice
+            libwnck-3.0
+            mate-desktop-2.0
+            sm
+        run: |
+          cppcheck --enable=${{env.checks}}                 \
+            -j ${{env.JOBS}}                                \
+            ${{env.defines}}                                \
+            $(pkg-config --cflags-only-I ${{env.packages}}) \
+            -i'gtk-layer-shell-build'                       \
+            -i'mate-panel/mate-submodules'                  \
+            .