package/clamav: add optional dependency to json-c

clamav has optional support for json-c:

$ output/host/usr/bin/i586-buildroot-linux-uclibc-readelf -a output/target/usr/lib/libclamav.so.7.1.1 | grep NEEDED
 0x00000001 (NEEDED)                     Shared library: [libltdl.so.7]
 0x00000001 (NEEDED)                     Shared library: [libssl.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libcrypto.so.1.0.0]
 0x00000001 (NEEDED)                     Shared library: [libz.so.1]
 0x00000001 (NEEDED)                     Shared library: [libjson-c.so.2]
 0x00000001 (NEEDED)                     Shared library: [libc.so.0]

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/clamav/clamav.mk

@@ -48,6 +48,13 @@ else
 CLAMAV_CONF_OPTS += --disable-bzip2
 endif
 
+ifeq ($(BR2_PACKAGE_JSON_C),y)
+CLAMAV_CONF_OPTS += --with-libjson=$(STAGING_DIR)/usr
+CLAMAV_DEPENDENCIES += json-c
+else
+CLAMAV_CONF_OPTS += --without-libjson
+endif
+
 ifeq ($(BR2_PACKAGE_LIBXML2),y)
 CLAMAV_CONF_OPTS += --with-xml=$(STAGING_DIR)/usr
 CLAMAV_DEPENDENCIES += libxml2