[gnome-usage] build: Fix post install script

[Petr Štětka <pstetka src gnome org>]

commit 8036b613c94e921fd2c54d46fed2adf3445a6a98
Author: Iñigo Martínez <inigomartinez gmail com>
Date:   Wed Dec 20 16:40:48 2017 +0100

    build: Fix post install script
    
    meson uses a post install script for compiling gsettings schemas
    and also updating the desktop database. However, it assumes that the
    data directory is the share directory under prefix, which might not
    be correct because the user can choose a different directory.
    
    This patch uses the data directory used by meson by passing it to
    the post install script.

 build-aux/meson/postinstall.sh | 6 +++---
 meson.build                    | 5 ++++-
 2 files changed, 7 insertions(+), 4 deletions(-)
---
diff --git a/build-aux/meson/postinstall.sh b/build-aux/meson/postinstall.sh
index 4500dcb..f68496f 100644
--- a/build-aux/meson/postinstall.sh
+++ b/build-aux/meson/postinstall.sh
@@ -1,10 +1,10 @@
 #!/bin/sh
 
 # Package managers set this so we don't need to run
-if [ -z "$DESTDIR" ]; then
+if [ -z "$DESTDIR" ] && [ $# -gt 0 ]; then
   echo Compiling GSettings schemas...
-  glib-compile-schemas ${MESON_INSTALL_PREFIX}/share/glib-2.0/schemas
+  glib-compile-schemas $1/glib-2.0/schemas
 
   echo Updating desktop database...
-  update-desktop-database -q ${MESON_INSTALL_PREFIX}/share/applications
+  update-desktop-database -q $1/applications
 fi
diff --git a/meson.build b/meson.build
index ef4d2c5..41c503c 100644
--- a/meson.build
+++ b/meson.build
@@ -27,4 +27,7 @@ subdir('po')
 subdir('external')
 subdir('src')
 
-meson.add_install_script ('build-aux/meson/postinstall.sh')
+meson.add_install_script(
+  join_paths('build-aux', 'meson', 'postinstall.sh'),
+  join_paths(get_option('prefix'), get_option('datadir'))
+)