package/netdata: link with libatomic when needed

netdata uses __atomic_fetch_add_2

Fixes:
 - http://autobuild.buildroot.org/results/1eb033ba7bf85ba3e25572a106f08faf49cd05b2

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>

package/netdata/netdata.mk

@@ -47,6 +47,10 @@ else
 NETDATA_CONF_OPTS += --disable-https
 endif
 
+ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
+NETDATA_CONF_ENV += LIBS=-latomic
+endif
+
 define NETDATA_INSTALL_INIT_SYSV
 	$(INSTALL) -D -m 755 package/netdata/S60netdata \
 		$(TARGET_DIR)/etc/init.d/S60netdata