[glib] meson: fix G_DIR_SEPARATOR* define on Windows

[Tim-Philipp Müller <tpm src gnome org>]

commit f25c7a2a6e25af878c586af926ec3c59f24964ad
Author: Tim-Philipp Müller <tim centricular com>
Date:   Wed Jan 10 15:57:46 2018 +0000

    meson: fix G_DIR_SEPARATOR* define on Windows
    
    Must double escape, once for Meson, once for the C string constant.
    
    https://bugzilla.gnome.org/show_bug.cgi?id=757284

 meson.build |    2 +-
 1 files changed, 1 insertions(+), 1 deletions(-)
---
diff --git a/meson.build b/meson.build
index a63dcb2..9b2cddc 100644
--- a/meson.build
+++ b/meson.build
@@ -997,7 +997,7 @@ if host_system == 'windows'
   else
     glibconfig_conf.set_quoted('g_pollfd_format', '%#x')
   endif
-  glibconfig_conf.set('g_dir_separator', '\\')
+  glibconfig_conf.set('g_dir_separator', '\\\\')
   glibconfig_conf.set('g_searchpath_separator', ';')
 else
   glibconfig_conf.set('g_pid_type', 'int')