jack2: needs C++ support

Fixes:

  http://autobuild.buildroot.org/results/ede/ede17f2fdb9b5cd4b974ef820d95b0eba863c420/

Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/jack2/Config.in

@@ -2,6 +2,7 @@ config BR2_PACKAGE_JACK2
 	bool "jack2"
 	depends on BR2_LARGEFILE # libsndfile
 	depends on BR2_TOOLCHAIN_HAS_THREADS # alsa-lib
+	depends on BR2_INSTALL_LIBSTDCPP
 	select BR2_PACKAGE_LIBSAMPLERATE
 	select BR2_PACKAGE_LIBSNDFILE
 	select BR2_PACKAGE_ALSA_LIB
@@ -18,5 +19,6 @@ config BR2_PACKAGE_JACK2
 
 	  http://jackaudio.org/
 
-comment "jack2 needs a toolchain w/ largefile and threads"
-	depends on !BR2_LARGEFILE || !BR2_TOOLCHAIN_HAS_THREADS
+comment "jack2 needs a toolchain w/ largefile, threads, C++"
+	depends on !BR2_LARGEFILE || !BR2_TOOLCHAIN_HAS_THREADS || \
+		!BR2_INSTALL_LIBSTDCPP