package/i2pd: fix static build with atomic

Use HAVE_CXX_ATOMICS_WITHOUT_LIB and HAVE_CXX_ATOMICS64_WITHOUT_LIB
variables to tell i2pd to check for atomic library and add it in
$(REQUIRED_LIBRARIES) if needed

Fixes:
 - http://autobuild.buildroot.org/results/dfffe21fab65b3fc81f449004a6771fd00efbc57

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Yann E. MORIN <yann.morin.1998@free.fr>

package/i2pd/i2pd.mk

@@ -22,7 +22,9 @@ I2PD_CONF_OPTS += -DWITH_GUI=OFF
 I2PD_CONF_OPTS += -DTHREADS_PTHREAD_ARG=OFF
 
 ifeq ($(BR2_TOOLCHAIN_HAS_LIBATOMIC),y)
-I2PD_CONF_OPTS += -DCMAKE_CXX_FLAGS="$(TARGET_CXXFLAGS) -latomic"
+I2PD_CONF_OPTS += \
+	-DHAVE_CXX_ATOMICS_WITHOUT_LIB=OFF \
+	-DHAVE_CXX_ATOMICS64_WITHOUT_LIB=OFF
 endif
 
 ifeq ($(BR2_STATIC_LIBS),y)