package/mono: needs C++

mono needs a working C++ compiler to get the exact type of size_t since
version 5.16.0.179 and
https://github.com/mono/mono/commit/d8af77551de1f59803a46946786e0f9a5eb5cb9d

Fixes:
 - http://autobuild.buildroot.org/results/ee6d037154127cc6572f06e9a78bae383ea381bc

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Tested-by: Angelo Compagnucci <angelo@amarulasolutions.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/mono/Config.in

@@ -12,6 +12,7 @@ config BR2_PACKAGE_MONO_ARCH_SUPPORTS
 config BR2_PACKAGE_MONO
 	bool "mono"
 	depends on BR2_PACKAGE_MONO_ARCH_SUPPORTS
+	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_TOOLCHAIN_HAS_THREADS
 	depends on !BR2_STATIC_LIBS
 	help
@@ -20,6 +21,7 @@ config BR2_PACKAGE_MONO
 
 	  http://download.mono-project.com/sources/mono/
 
-comment "mono needs a toolchain w/ threads, dynamic library"
+comment "mono needs a toolchain w/ C++, threads, dynamic library"
 	depends on BR2_PACKAGE_MONO_ARCH_SUPPORTS
-	depends on !BR2_TOOLCHAIN_HAS_THREADS || BR2_STATIC_LIBS
+	depends on !BR2_INSTALL_LIBSTDCPP || \
+		!BR2_TOOLCHAIN_HAS_THREADS || BR2_STATIC_LIBS