[libhandy/mcatanzaro/#290] Don't install glade files outside prefix

[Michael Catanzaro <mcatanzaro src gnome org>]

commit a90a399ba3bd6c9e1d8e417126153d6d6dc1e0e1
Author: Michael Catanzaro <mcatanzaro gnome org>
Date:   Wed Jun 10 15:26:15 2020 -0500

    Don't install glade files outside prefix
    
    See https://www.bassi.io/articles/2018/03/15/pkg-config-and-paths/
    
    Fixes #290

 glade/meson.build | 18 ++++--------------
 1 file changed, 4 insertions(+), 14 deletions(-)
---
diff --git a/glade/meson.build b/glade/meson.build
index e055f65c..cba9a364 100644
--- a/glade/meson.build
+++ b/glade/meson.build
@@ -1,21 +1,11 @@
 if glade_catalog
 
-# This is needed to work around this issue in Glade:
-# https://gitlab.gnome.org/GNOME/glade/issues/379
-is_flatpak_app = get_option('prefix') == '/app'
-
 glade_xml          = 'libhandy.xml'
-if (is_flatpak_app)
-  module_dir       = libdir / 'glade' / 'modules'
-else
-  module_dir       = gladeui_dep.get_pkgconfig_variable('moduledir')
-endif
+module_dir         = gladeui_dep.get_pkgconfig_variable('moduledir',
+                                                        define_variable: ['libdir', get_option('libdir')])
 dtd                = meson.current_source_dir() / 'glade-catalog.dtd'
-if (is_flatpak_app)
-  glade_catalogdir = datadir / 'glade' / 'catalogs'
-else
-  glade_catalogdir = gladeui_dep.get_pkgconfig_variable('catalogdir')
-endif
+glade_catalogdir   = gladeui_dep.get_pkgconfig_variable('catalogdir',
+                                                        define_variable: ['datadir', get_option('datadir')])
 
 libglade_hdy_sources = [
   'glade-hdy-carousel.c',