package/redis-plus-plus: disable shared library build with BR2_STATIC_LIBS=y

Fixes:
http://autobuild.buildroot.net/results/6d3/6d310d52dbfe076cd470be71f02de32fb47fa904/
in combination with the bump of hiredis to 1.2.0 which contains
improvements for static builds.

Signed-off-by: Bernd Kuhls <bernd@kuhls.net>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/redis-plus-plus/redis-plus-plus.mk

@@ -12,6 +12,7 @@ REDIS_PLUS_PLUS_INSTALL_STAGING = YES
 REDIS_PLUS_PLUS_DEPENDENCIES = hiredis
 
 REDIS_PLUS_PLUS_CONF_OPTS = \
+	-DREDIS_PLUS_PLUS_BUILD_SHARED=$(if $(BR2_STATIC_LIBS),OFF,ON) \
 	-DREDIS_PLUS_PLUS_BUILD_TEST=OFF
 
 # since version 1.3.0, by default, redis-plus-plus is built with the