Code must only ever include glib.h indirectly via the glib-compat.h
header file, because we will need some macros set before glib.h is
pulled in. Adding extra includes of glib.h will (soon) cause compile
failures such as:

In file included from /home/berrange/src/virt/qemu/include/qemu/osdep.h:107,
                 from /home/berrange/src/virt/qemu/include/qemu/iova-tree.h:26,
                 from util/iova-tree.c:13:
/home/berrange/src/virt/qemu/include/glib-compat.h:22: error: "GLIB_VERSION_MIN_REQUIRED" redefined [-Werror]
 #define GLIB_VERSION_MIN_REQUIRED GLIB_VERSION_2_40

In file included from /usr/include/glib-2.0/glib/gtypes.h:34,
                 from /usr/include/glib-2.0/glib/galloca.h:32,
                 from /usr/include/glib-2.0/glib.h:30,
                 from util/iova-tree.c:12:
/usr/include/glib-2.0/glib/gversionmacros.h:237: note: this is the location of the previous definition
 # define GLIB_VERSION_MIN_REQUIRED      (GLIB_VERSION_CUR_STABLE)

Furthermore, the osdep.h include should always be done directly from the
.c file rather than indirectly via any .h file.
Reviewed-by: NPhilippe Mathieu-Daudé <f4bug@amsat.org>
Signed-off-by: NDaniel P. Berrangé <berrange@redhat.com>