[gtk/matthiasc/for-master] build: Try to fix docs+subprojects

[Matthias Clasen <matthiasc src gnome org>]

commit 91c8f6b7df62e3b6eb4aac8eb797d67569cdec4d
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Sep 30 16:21:39 2020 -0400

    build: Try to fix docs+subprojects
    
    Apparently, subprojects don't have pkgconfig variables :(

 docs/reference/meson.build | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)
---
diff --git a/docs/reference/meson.build b/docs/reference/meson.build
index a308cc4c87..4536addda4 100644
--- a/docs/reference/meson.build
+++ b/docs/reference/meson.build
@@ -1,11 +1,11 @@
 if get_option('gtk_doc')
-  glib_prefix = dependency('glib-2.0').get_pkgconfig_variable('prefix')
+  glib_prefix = dependency('glib-2.0').get_variable(pkgconfig: 'prefix', default_value: '/usr')
   glib_docpath = join_paths(glib_prefix, 'share', 'gtk-doc', 'html')
 
-  cairo_prefix = dependency('cairo-gobject').get_pkgconfig_variable('prefix')
+  cairo_prefix = dependency('cairo-gobject').get_variable(pkgconfig: 'prefix', default_value: '/usr')
   cairo_docpath = join_paths(cairo_prefix, 'share', 'gtk-doc', 'html', 'cairo')
 
-  gdkpixbuf_prefix = dependency('gdk-pixbuf-2.0').get_pkgconfig_variable('prefix')
+  gdkpixbuf_prefix = dependency('gdk-pixbuf-2.0').get_variable(pkgconfig: 'prefix', default_value: '/usr')
   gdkpixbuf_docpath = join_paths(gdkpixbuf_prefix, 'share', 'gtk-doc', 'html', 'gdk-pixbuf')
 
   docpath = join_paths(gtk_datadir, 'gtk-doc', 'html')