build: Fix stylesheet dependency for GTK gresources

Since the stylesheet targets were not stored in an array, only the
main variant stylesheet target was a dependency for the theme
gresource. This could result the build to fail, if the dark
stylesheet was not generated in time.

Fixes: #170

common/gtk-3.0/meson.build

@@ -30,8 +30,11 @@ input_scss_dark = configure_file(
     'sass_path' : meson.current_source_dir() / 'sass',
   }
 )
+
 output_css_dark = 'gtk-main-dark.css'
-gtk3_stylesheet = custom_target(
+gtk3_stylesheets = []
+
+gtk3_stylesheets += custom_target(
   output_css_dark,
   input : input_scss_dark,
   output : output_css_dark,
@@ -54,7 +57,7 @@ foreach variant : get_option('variants')
       }
     )
 
-    gtk3_stylesheet = custom_target(
+    gtk3_stylesheets += custom_target(
       output_css,
       input : input_scss,
       output : output_css,
@@ -110,7 +113,7 @@ foreach variant : get_option('variants')
       '--target=@OUTPUT@',
       '@INPUT@'
     ],
-    depends : [gtk3_assets, gtk3_hidpi_assets, gtk3_stylesheet],
+    depends : [gtk3_assets, gtk3_hidpi_assets, gtk3_stylesheets],
     depend_files : [gtk3_asset_files, gtk3_hidpi_asset_files],
     build_by_default : true
   )

common/gtk-4.0/meson.build

@@ -62,8 +62,11 @@ input_scss_dark = configure_file(
     'sass_path' : meson.current_source_dir() / gtk4_ver / 'sass',
   }
 )
+
 output_css_dark = 'gtk-main-dark.css'
-gtk4_stylesheet = custom_target(
+gtk4_stylesheets = []
+
+gtk4_stylesheets += custom_target(
   output_css_dark,
   input : input_scss_dark,
   output : output_css_dark,
@@ -86,7 +89,7 @@ foreach variant : get_option('variants')
       }
     )
 
-    gtk4_stylesheet = custom_target(
+    gtk4_stylesheets += custom_target(
       output_css,
       input : input_scss,
       output : output_css,
@@ -143,7 +146,7 @@ foreach variant : get_option('variants')
       '--target=@OUTPUT@',
       '@INPUT@'
     ],
-    depends : [gtk4_assets, gtk4_hidpi_assets, gtk4_stylesheet],
+    depends : [gtk4_assets, gtk4_hidpi_assets, gtk4_stylesheets],
     depend_files : [gtk4_asset_files, gtk4_hidpi_asset_files],
     build_by_default : true
   )