[glib/wip/meson] meson: Fix building as a subproject

[Thibault Saunier <tsaunier src gnome org>]

commit cc3ec2c212297d195ec8d28a052d6a81591a9591
Author: Thibault Saunier <thibault saunier osg samsung com>
Date:   Fri Jun 23 12:00:13 2017 -0400

    meson: Fix building as a subproject
    
    meson.source_root() returns the toplevel source directory
    of the toplevel project, thus the paths were wrong when using
    it. Simply using files() gets us the right path
    
    https://bugzilla.gnome.org/show_bug.cgi?id=784133

 gio/meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/gio/meson.build b/gio/meson.build
index 603b0b3..31153bb 100644
--- a/gio/meson.build
+++ b/gio/meson.build
@@ -732,7 +732,7 @@ if libelf.found()
 endif
 
 gconstructor_as_data_h = custom_target('gconstructor_as_data.h',
-    input : ['data-to-c.py', meson.source_root() + '/glib/gconstructor.h'],
+    input : ['data-to-c.py', files('../glib/gconstructor.h')],
     output : ['gconstructor_as_data.h'],
     command : [python, '@INPUT0@', '@INPUT1@', 'gconstructor_code', '@OUTPUT@'])