Bug#597680: "cast discards qualifiers from pointer target type"

[Max Kellermann]

Package: libglib2.0-dev
Version: 2.24.2-1

When compiling with gcc 4.4.4-8 and all warning flags enabled (and
-Werror), including GLib headers emits the following warning:

 /usr/include/glib-2.0/glib/gthread.h: In function 'g_once_init_enter':
 /usr/include/glib-2.0/glib/gthread.h:348: error: cast discards qualifiers from pointer target type

This breaks the build in all of my projects, because I use -Werror.
Using -isystem instead of -I could probably work around that header
bug, but I'm using pkg-config to configure GLib, and GLib's pkg-config
files use -I.