package/woff2: add a comment for C++

woff2 depends on C++ so add a comment if C++ is not enabled

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Reviewed-by: Adrian Perez de Castro <aperez@igalia.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/woff2/Config.in

@@ -7,3 +7,6 @@ config BR2_PACKAGE_WOFF2
 	  typically used for Web fonts
 
 	  https://github.com/google/woff2
+
+comment "woff2 needs a toolchain w/ C++"
+	depends on !BR2_INSTALL_LIBSTDCPP