msgpack: disable for ARC

msgpack uses the __sync_fetch_and_add() atomic primitive that is not
available for ARC. Fixes:
http://autobuild.buildroot.net/results/829/8292e67354602738cae12d8ebea83b513ba35482/

Signed-off-by: Gustavo Zacarias <gustavo@zacarias.com.ar>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/msgpack/Config.in

@@ -1,6 +1,7 @@
 config BR2_PACKAGE_MSGPACK
 	bool "msgpack"
 	depends on BR2_INSTALL_LIBSTDCPP
+	depends on !BR2_arc # atomic builtins
 	help
 	  MessagePack is an efficient binary serialization format.
 
@@ -11,3 +12,4 @@ config BR2_PACKAGE_MSGPACK
 
 comment "msgpack needs a toolchain w/ C++"
 	depends on !BR2_INSTALL_LIBSTDCPP
+	depends on !BR2_arc

package/python-msgpack/Config.in

@@ -3,6 +3,7 @@ config BR2_PACKAGE_PYTHON_MSGPACK
 	depends on BR2_PACKAGE_PYTHON
 	select BR2_PACKAGE_MSGPACK
 	depends on BR2_INSTALL_LIBSTDCPP # msgpack
+	depends on !BR2_arc # msgpack - atomic builtins
 	help
 	  MessagePack (http://msgpack.org/) is a fast, compact binary
 	  serialization format, suitable for similar data to JSON.
@@ -14,3 +15,4 @@ config BR2_PACKAGE_PYTHON_MSGPACK
 comment "python-msgpack needs a toolchain w/ C++"
 	depends on BR2_PACKAGE_PYTHON
 	depends on !BR2_INSTALL_LIBSTDCPP
+	depends on !BR2_arc