package/gensio: add C++ optional dependency

C++ is available since 2.3.0 and
https://github.com/cminyard/gensio/commit/3fda483f15a2668f9e2396517cdbf09693e6e3ff

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/gensio/gensio.mk

@@ -13,6 +13,12 @@ GENSIO_CONF_OPTS = \
 	--without-swig \
 	--without-python
 
+ifeq ($(BR2_INSTALL_LIBSTDCPP),y)
+GENSIO_CONF_OPTS += --with-cplusplus
+else
+GENSIO_CONF_OPTS += --without-cplusplus
+endif
+
 ifeq ($(BR2_PACKAGE_ALSA_LIB_PCM),y)
 GENSIO_DEPENDENCIES += alsa-lib
 GENSIO_CONF_OPTS += --with-alsa