[sysprof] build: require itstool if installing help files

[Christian Hergert <chergert src gnome org>]

commit 59942e6fa62d8af73e4fa169df4b9d486f47a452
Author: Christian Hergert <chergert redhat com>
Date:   Thu Feb 20 10:59:31 2020 -0800

    build: require itstool if installing help files

 help/meson.build | 2 ++
 1 file changed, 2 insertions(+)
---
diff --git a/help/meson.build b/help/meson.build
index ec3e5b6..b2aec10 100644
--- a/help/meson.build
+++ b/help/meson.build
@@ -1,4 +1,6 @@
 if get_option('help')
+  find_program('itstool', required: true)
+
   gnome.yelp('sysprof',
     sources: ['index.page', 'introduction.page', 'profiling.page', 'faq.page', 'legal.xml'],
   )