pkg-perl: fix PERL_INC in generated Makefile

when directly setting PERL_INC with a path to STAGING_DIR,
the generated Makefile contains a PERL_INC with a path to HOST_DIR

when setting PERL_ARCHLIB, PERL_INC is generated as $(PERL_ARCHLIB)/CORE

fix this kind of build failure:
http://autobuild.buildroot.net/results/8934f2c203f8b61519dba94188985f1a9261de9a/

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

package/pkg-perl.mk

@@ -102,7 +102,7 @@ define $(2)_CONFIGURE_CMDS
 			LD="$$(TARGET_CC)" \
 			LDDLFLAGS="-shared $$(TARGET_LDFLAGS)" \
 			LDFLAGS="$$(TARGET_LDFLAGS)" \
-			PERL_INC=$$(STAGING_DIR)/usr/lib/perl5/$$(PERL_VERSION)/$$(PERL_ARCHNAME)/CORE \
+			PERL_ARCHLIB=$$(STAGING_DIR)/usr/lib/perl5/$$(PERL_VERSION)/$$(PERL_ARCHNAME) \
 			DESTDIR=$$(TARGET_DIR) \
 			INSTALLDIRS=vendor \
 			INSTALLVENDORLIB=/usr/lib/perl5/site_perl/$$(PERL_VERSION) \