[baobab] build: Use python3 found by meson to run build-aux/post-install.py

[Ting-Wei Lan <lantw src gnome org>]

commit db68f3a0a11b88da8fc6d94ea9d2d11baefb239d
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Wed Dec 27 20:32:28 2017 +0800

    build: Use python3 found by meson to run build-aux/post-install.py
    
    https://bugzilla.gnome.org/show_bug.cgi?id=791980

 build-aux/post-install.py |    2 +-
 meson.build               |    4 +++-
 2 files changed, 4 insertions(+), 2 deletions(-)
---
diff --git a/build-aux/post-install.py b/build-aux/post-install.py
index c1faf09..69d526a 100755
--- a/build-aux/post-install.py
+++ b/build-aux/post-install.py
@@ -1,4 +1,4 @@
-#!/usr/bin/python3
+#!/usr/bin/env python3
 
 import os
 import pathlib
diff --git a/meson.build b/meson.build
index 44bb3d7..7313cec 100644
--- a/meson.build
+++ b/meson.build
@@ -7,6 +7,7 @@ project(
 
 gnome = import('gnome')
 i18n = import('i18n')
+python3 = import('python3')
 
 glib = dependency('glib-2.0', version: '>=2.44')
 gio = dependency('gio-2.0', version: '>=2.44')
@@ -26,7 +27,8 @@ conf.set_quoted('GNOMELOCALEDIR', join_paths(get_option('prefix'), get_option('d
 configure_file(output: 'config.h', configuration: conf)
 config_h_dir = include_directories('.')
 
-meson.add_install_script(join_paths('build-aux', 'post-install.py'))
+meson.add_install_script(python3.find_python().path(),
+  join_paths(meson.source_root(), 'build-aux', 'post-install.py'))
 
 subdir('data')
 subdir('help')