libpv: disallow glib features from after 2.56

Enforce that the first glib.h include is done via glib-helper.h for libpv
so that glib version checks are in place.

Change zdump and pvattest such that they never include glibstuff before
libpv/glib-helper.h

Reviewed-by: Jan Hoeppner <hoeppner@linux.ibm.com>
Signed-off-by: Steffen Eiden <seiden@linux.ibm.com>

zdump/dfi_pv_elf.c

@@ -21,7 +21,6 @@
 #include <elf.h>
 #include <errno.h>
 
-#include <glib.h>
 #include <openssl/bio.h>
 #include <openssl/crypto.h>