Suppress memory leak reports from GTK CSS drawing functions

We don't seem to be doing anything wrong, but ASAN detects many such
leaks as soon as we call functions such as gtk_css_style_render_icon()
(used by wxRendererGTK::DrawCheckBox()) and several others.

misc/suppressions/lsan

@@ -16,3 +16,30 @@ leak:atk_bridge_adaptor_init
 # Leak in a function called from gtk_init_check() when using X RandR extension.
 # Requires debug symbols for libxrandr2.
 leak:doGetScreenResources
+
+# There seem to be several actual (although not unbound) leaks inside Cairo or
+# pixman resulting in memory leak reports when calling various drawing
+# functions using CSS internally.
+leak:_cairo_image_surface_create_for_pixman_image
+leak:_cairo_image_surface_create_with_pixman_format
+leak:_cairo_surface_create_similar_image
+leak:_cairo_surface_create_similar_image
+leak:gtk_css_image_surface_draw
+leak:_gtk_css_image_draw
+
+leak:create_bits
+leak:_pixman_bits_image_init
+leak:create_bits_image_internal
+leak:_cairo_image_surface_create_with_pixman_format
+leak:_cairo_surface_create_similar_image
+leak:_cairo_surface_create_similar_image
+leak:gtk_css_image_surface_draw
+leak:_gtk_css_image_draw
+
+leak:_pixman_image_allocate
+leak:create_bits_image_internal
+leak:_cairo_image_surface_create_with_pixman_format
+leak:_cairo_surface_create_similar_image
+leak:_cairo_surface_create_similar_image
+leak:gtk_css_image_surface_draw
+leak:_gtk_css_image_draw