package/qpdf: add optional gnutls dependency

gnutls is an optional dependency since version 9.1.0 and
https://github.com/qpdf/qpdf/commit/88bedb41fe82df312d62e364a5a216b62fc8807c

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/qpdf/qpdf.mk

@@ -13,4 +13,11 @@ QPDF_DEPENDENCIES = host-pkgconf zlib jpeg
 
 QPDF_CONF_OPTS = --without-random
 
+ifeq ($(BR2_PACKAGE_GNUTLS),y)
+QPDF_CONF_OPTS += --enable-crypto-gnutls
+QPDF_DEPENDENCIES += gnutls
+else
+QPDF_CONF_OPTS += --disable-crypto-gnutls
+endif
+
 $(eval $(autotools-package))