boost: Add comment when C++ is missing

[Peter: move above boost option so sub options gets indented]
Signed-off-by: Stephan Thamm <thammi@chaossource.net>
Acked-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>
Signed-off-by: Peter Korsgaard <jacmet@sunsite.dk>

package/boost/Config.in

@@ -1,3 +1,6 @@
+comment "boost requires a toolchain with C++ support enabled"
+	depends on !BR2_INSTALL_LIBSTDCPP
+
 config BR2_PACKAGE_BOOST
 	bool "boost"
 	depends on BR2_INSTALL_LIBSTDCPP