python-service-identity: add missing BR2_INSTALL_LIBSTDCPP dependency

python-service-identity selects python-pyopenssl and python-pyasn, both
of which depend on C++ support, but this dependency was not propagated
to python-service-identity causing the following kconfig warning:

warning: (BR2_PACKAGE_PYTHON_SERVICE_IDENTITY) selects BR2_PACKAGE_PYTHON_PYOPENSSL which has unmet direct dependencies ((BR2_PACKAGE_PYTHON || BR2_PACKAGE_PYTHON3) && BR2_INSTALL_LIBSTDCPP)
warning: (BR2_PACKAGE_PYTHON_SERVICE_IDENTITY) selects BR2_PACKAGE_PYTHON_PYASN which has unmet direct dependencies ((BR2_PACKAGE_PYTHON || BR2_PACKAGE_PYTHON3) && BR2_INSTALL_LIBSTDCPP)
warning: (BR2_PACKAGE_PYTHON_SERVICE_IDENTITY) selects BR2_PACKAGE_PYTHON_PYASN_MODULES which has unmet direct dependencies ((BR2_PACKAGE_PYTHON || BR2_PACKAGE_PYTHON3) && BR2_INSTALL_LIBSTDCPP)

Cc: Yegor Yefremov <yegorslists@googlemail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Reviewed-by: Yegor Yefremov <yegorslists@googlemail.com>
[Thomas: add Config.in comment.]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/python-service-identity/Config.in

@@ -4,7 +4,11 @@ config BR2_PACKAGE_PYTHON_SERVICE_IDENTITY
 	select BR2_PACKAGE_PYTHON_PYASN # runtime
 	select BR2_PACKAGE_PYTHON_PYASN_MODULES # runtime
 	select BR2_PACKAGE_PYTHON_PYOPENSSL # runtime
+	depends on BR2_INSTALL_LIBSTDCPP # python-pyopenssl, python-pyasn
 	help
 	  Service identity verification for pyOpenSSL.
 
 	  https://pypi.python.org/pypi/service_identity
+
+comment "python-service-identify needs a toolchain w/ C++"
+	depends on !BR2_INSTALL_LIBSTDCPP