[libgit2-glib] Fix meson_vapi_link.py to respect DESTDIR

[Alberto Fanjul <albfan src gnome org>]

commit 7f63349fd0405439532f2ff0896a3697c73ccaaf
Author: Michał Górny <mgorny gentoo org>
Date:   Thu Feb 27 15:20:20 2020 +0100

    Fix meson_vapi_link.py to respect DESTDIR
    
    Fixes #5

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index 6d314b5..3a423b3 100644
--- a/meson.build
+++ b/meson.build
@@ -135,7 +135,7 @@ if enable_vapi
   assert(enable_gir, 'vapi support was requested, but introspection support is mandatory.')
   assert(add_languages('vala', required: false), 'vapi support was requested, but vala not found.')
 
-  meson.add_install_script('meson_vapi_link.py', libgit2_glib_datadir)
+  meson.add_install_script('meson_vapi_link.py', get_option('datadir'))
 endif
 
 # Check for libgit2 ssh support