perl: fix build of native modules

CORE/vutil.h is required when the host perl version is 5.20
see http://autobuild.buildroot.net/results/c3d/c3d48c3b3d6c1e616d8e20a2f65d8ba33abe61da/

Signed-off-by: Francois Perrad <francois.perrad@gadz.org>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/perl/perl.mk

@@ -117,6 +117,7 @@ endef
 define PERL_ADD_CORE_H
 	touch $(STAGING_DIR)/usr/lib/perl5/$(PERL_VERSION)/$(PERL_ARCHNAME)/CORE/patchlevel-debian.h
 	touch $(STAGING_DIR)/usr/lib/perl5/$(PERL_VERSION)/$(PERL_ARCHNAME)/CORE/cc_runtime.h
+	touch $(STAGING_DIR)/usr/lib/perl5/$(PERL_VERSION)/$(PERL_ARCHNAME)/CORE/vutil.h
 endef
 
 PERL_POST_INSTALL_STAGING_HOOKS += PERL_ADD_CORE_H