shairport-sync: requires C++

Fixes:
http://autobuild.buildroot.net/results/122/122d6cedf0205e8db27d498d6a2a839e11e7b6f2/
http://autobuild.buildroot.net/results/bef/bef5fb328e6688107496cb213d8aeeca527abf03/

Cc: Jörg Krause <joerg.krause@embedded.rocks>
Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/shairport-sync/Config.in

@@ -2,6 +2,7 @@ config BR2_PACKAGE_SHAIRPORT_SYNC
 	bool "shairport-sync"
 	depends on BR2_USE_MMU # libdaemon
 	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL
+	depends on BR2_INSTALL_LIBSTDCPP
 	select BR2_PACKAGE_ALSA_LIB
 	select BR2_PACKAGE_ALSA_LIB_MIXER
 	select BR2_PACKAGE_LIBCONFIG
@@ -34,6 +35,6 @@ config BR2_PACKAGE_SHAIRPORT_SYNC_LIBSOXR
 
 endif
 
-comment "shairport-sync needs a toolchain w/ NPTL"
+comment "shairport-sync needs a toolchain w/ C++, NPTL"
 	depends on BR2_USE_MMU
-	depends on !BR2_TOOLCHAIN_HAS_THREADS_NPTL
+	depends on !BR2_INSTALL_LIBSTDCPP || !BR2_TOOLCHAIN_HAS_THREADS_NPTL