meson: Avoid using relative paths to po directory

Replace the relative path to the po directory with a toplevel definition
of po_dir and use that instead.

https://gitlab.gnome.org/GNOME/gnome-shell/merge_requests/507

data/meson.build

@@ -24,7 +24,7 @@ foreach desktop_file : desktop_files
       configuration: desktopconf
     ),
     output: desktop_file,
-    po_dir: '../po',
+    po_dir: po_dir,
     install: true,
     install_dir: desktopdir,
     type: 'desktop'

meson.build

@@ -243,6 +243,8 @@ libgvc = subproject('gvc',
 )
 libgvc_gir = libgvc.get_variable('libgvc_gir')
 
+po_dir = join_paths(meson.current_source_dir(), 'po')
+
 subdir('js')
 subdir('src')
 subdir('po')

src/calendar-server/meson.build

@@ -30,7 +30,7 @@ configure_file(
 i18n.merge_file('evolution-calendar.desktop',
   input: 'evolution-calendar.desktop.in',
   output: 'evolution-calendar.desktop',
-  po_dir: '../../po',
+  po_dir: po_dir,
   install: true,
   install_dir: desktopdir,
   type: 'desktop'