package/kf5-kcoreaddons: fix build with atomic

Fixes:
 - http://autobuild.buildroot.org/results/d17c2fb420e395b995b2c2eef387f0c66e89c96c

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

package/kf5/kf5-kcoreaddons/kf5-kcoreaddons.mk

@@ -13,4 +13,11 @@ KF5_KCOREADDONS_LICENSE_FILES = COPYING.LIB
 KF5_KCOREADDONS_DEPENDENCIES = kf5-extra-cmake-modules qt5tools
 KF5_KCOREADDONS_INSTALL_STAGING = YES
 
+KF5_KCOREADDONS_CXXFLAGS = $(TARGET_CXXFLAGS)
+KF5_KCOREADDONS_CONF_OPTS = -DCMAKE_CXX_FLAGS="$(KF5_KCOREADDONS_CXXFLAGS)"
+
+ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
+KF5_KCOREADDONS_CXXFLAGS += -latomic
+endif
+
 $(eval $(cmake-package))