package/opencv3: use BR2_TOOLCHAIN_HAS_LIBATOMIC

It uses __atomic_fetch_add_4 so libatomic must be pulled in if
necessary. Fixes
http://autobuild.buildroot.net/results/652/6521223b426c3cb4dfefab27bc6021900db6910e/

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

package/opencv3/Config.in

@@ -1,6 +1,7 @@
 menuconfig BR2_PACKAGE_OPENCV3
 	bool "opencv3"
 	select BR2_PACKAGE_ZLIB
+	depends on BR2_TOOLCHAIN_HAS_ATOMIC
 	depends on BR2_TOOLCHAIN_HAS_THREADS_NPTL
 	depends on BR2_INSTALL_LIBSTDCPP
 	depends on BR2_USE_WCHAR
@@ -335,6 +336,7 @@ config BR2_PACKAGE_OPENCV3_INSTALL_DATA
 endif # BR2_PACKAGE_OPENCV3
 
 comment "opencv3 needs a toolchain w/ C++, NPTL, wchar, dynamic library"
+	depends on BR2_TOOLCHAIN_HAS_ATOMIC
 	depends on !BR2_INSTALL_LIBSTDCPP || \
 		!BR2_USE_WCHAR || \
 		!BR2_TOOLCHAIN_HAS_THREADS_NPTL || \

package/opencv3/opencv3.mk

@@ -10,6 +10,11 @@ OPENCV3_INSTALL_STAGING = YES
 OPENCV3_LICENSE = BSD-3c
 OPENCV3_LICENSE_FILES = LICENSE
 
+# Uses __atomic_fetch_add_4
+ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
+OPENCV3_CONF_OPTS += -DCMAKE_CXX_FLAGS="-latomic"
+endif
+
 # OpenCV component options
 OPENCV3_CONF_OPTS += \
 	-DBUILD_DOCS=OFF \