package/zmqpp: link with libatomic when needed

Fixes
http://autobuild.buildroot.net/results/c32/c32b9b8dd00d6f6d3db27fae9d8de758a4f25138/

Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>

package/zmqpp/zmqpp.mk

@@ -13,6 +13,10 @@ ZMQPP_LICENSE_FILES = LICENSE
 ZMQPP_MAKE_OPTS = LD="$(TARGET_CXX)" BUILD_PATH=./build PREFIX=/usr
 ZMQPP_LDFLAGS = $(TARGET_LDFLAGS) -lpthread
 
+ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
+ZMQPP_LDFLAGS += -latomic
+endif
+
 ifeq ($(BR2_PACKAGE_ZMQPP_CLIENT),y)
 ZMQPP_DEPENDENCIES += boost
 endif