[gnome-software/wip/lantw/freebsd-memory-total] build: Update _XOPEN_SOURCE to the latest version

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

commit c7f7ebc35dbd376cda27a31083343d9b75ceb027
Author: Ting-Wei Lan <lantw src gnome org>
Date:   Wed Jan 31 03:45:27 2018 +0800

    build: Update _XOPEN_SOURCE to the latest version
    
    Setting _XOPEN_SOURCE to 500 disables C99 on FreeBSD and causes implicit
    declaration warnings to be shown during compilation.

 meson.build | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/meson.build b/meson.build
index d20fc864..b5372b8e 100644
--- a/meson.build
+++ b/meson.build
@@ -90,7 +90,7 @@ add_global_link_arguments(
 )
 
 # Needed for PATH_MAX and symlink()
-add_project_arguments('-D_XOPEN_SOURCE=500', language : 'c')
+add_project_arguments('-D_XOPEN_SOURCE=700', language : 'c')
 
 appstream_glib = dependency('appstream-glib', version : '>= 0.7.3')
 gdk_pixbuf = dependency('gdk-pixbuf-2.0', version : '>= 2.31.5')