benejson: needs c++

pull.cpp doesn't look like vanilla C
Fixes local tests (no autobuilder tests to show off atm).

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/benejson/Config.in

@@ -1,5 +1,6 @@
 config BR2_PACKAGE_BENEJSON
 	bool "benejson"
+	depends on BR2_INSTALL_LIBSTDCPP
 	help
 	  benejson is a buffering SAX-style JSON parser library.
 	  The library package contains 3 major components:
@@ -9,3 +10,6 @@ config BR2_PACKAGE_BENEJSON
 	  - Core: The parsing core with minimal dependencies
 
 	  https://codehero.github.io/benejson/
+
+comment "benejson needs a toolchain w/ C++"
+	depends on !BR2_INSTALL_LIBSTDCPP