build: Add a sassc feature

Add an option to disable css rebuilds. This allows
to build GTK from release tarballs (Which are including
the css) without a sassc dependency.

gtk/meson.build

@@ -838,20 +838,24 @@ gtk_gresources_xml = configure_file(output: 'gtk.gresources.xml',
 
 # Build the theme files
 sassc = find_program('sassc', required: false)
-if not sassc.found()
+if not sassc.found() and not get_option('sassc').disabled()
   subproject('sassc')
-  sassc = find_program('sassc', required: true)
+  sassc = find_program('sassc', required: get_option('sassc').enabled())
 endif
 
-sassc_opts = [ '-a', '-M', '-t', 'compact' ]
+if sassc.found()
+  sassc_opts = [ '-a', '-M', '-t', 'compact' ]
 
-subdir('theme/Adwaita')
-subdir('theme/HighContrast')
+  subdir('theme/Adwaita')
+  subdir('theme/HighContrast')
 
-theme_deps = [
-  adwaita_theme_deps,
-  hc_theme_deps,
-]
+  theme_deps = [
+    adwaita_theme_deps,
+    hc_theme_deps,
+  ]
+else
+  theme_deps = []
+endif
 
 gtkresources = gnome.compile_resources('gtkresources',
   gtk_gresources_xml,

meson_options.txt

@@ -78,9 +78,14 @@ option('tracker',
 
 option('colord',
        type: 'feature',
-       value : 'disabled',
+       value: 'disabled',
        description : 'Build colord support for the CUPS printing backend')
 
+option('sassc',
+       type: 'feature',
+       value: 'auto',
+       description: 'Rebuild themes using sassc')
+
 # Documentation and introspection
 
 option('gtk_doc',