package/openzwave: fix example build

-std=c++11 has been wrongly removed from CFLAGS since commit
c5ca521e232eae31276e7a12d17f0cf9d9c0108f resulting in the following
build failure:

In file included from /home/buildroot/autobuild/run/instance-1/output-1/build/openzwave-62444b0f979c337d2091d77d89cf63c2ae9775cf/cpp/src/Driver.h:38:0,
                 from /home/buildroot/autobuild/run/instance-1/output-1/build/openzwave-62444b0f979c337d2091d77d89cf63c2ae9775cf/cpp/src/Manager.h:39,
                 from Main.cpp:37:
/home/buildroot/autobuild/run/instance-1/output-1/build/openzwave-62444b0f979c337d2091d77d89cf63c2ae9775cf/cpp/src/Node.h:566:32: error: 'std::shared_ptr' has not been declared
    void SetProductDetails(std::shared_ptr<Internal::ProductDescriptor> product);
                                ^

Fixes:
 - http://autobuild.buildroot.org/results/a7999ffe3b93391b9a20dcfa3ddd9d21daf0cace

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Arnout Vandecappelle (Essensium/Mind) <arnout@mind.be>

package/openzwave/openzwave.mk

@@ -31,8 +31,8 @@ OPENZWAVE_MAKE_OPTS = \
 	pkgconfigdir=/usr/lib/pkgconfig \
 	sysconfdir=/etc/openzwave \
 	DOXYGEN= \
-	DEBUG_CFLAGS="-fPIC" \
-	RELEASE_CFLAGS="-fPIC" \
+	DEBUG_CFLAGS="-fPIC -std=c++11" \
+	RELEASE_CFLAGS="-fPIC -std=c++11" \
 	USE_BI_TXML=0
 
 ifeq ($(BR2_PACKAGE_HAS_UDEV),y)