[gtk] build: Add a sassc feature

[Matthias Clasen <matthiasc src gnome org>]

commit 2b6b35d91fb2a367d2e39a7b7b36d08c604c6195
Author: Matthias Clasen <mclasen redhat com>
Date:   Sat Jan 9 01:28:11 2021 -0500

    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   | 22 +++++++++++++---------
 meson_options.txt |  7 ++++++-
 2 files changed, 19 insertions(+), 10 deletions(-)
---
diff --git a/gtk/meson.build b/gtk/meson.build
index 9f07d3d5f0..f1fd696297 100644
--- a/gtk/meson.build
+++ b/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,
diff --git a/meson_options.txt b/meson_options.txt
index 24a61511d7..71b01ec5c8 100644
--- a/meson_options.txt
+++ b/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',