package/grantlee: fix build with Qt 5.x

Fixes:
 - http://autobuild.buildroot.org/results/f0ec288fe47b6e8cf16179e3f281cf9caebb8fe9

Signed-off-by: Fabrice Fontaine <fontaine.fabrice@gmail.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>

package/grantlee/grantlee.mk

@@ -11,4 +11,9 @@ GRANTLEE_LICENSE = LGPL-2.1+
 GRANTLEE_LICENSE_FILES = COPYING.LIB
 GRANTLEE_DEPENDENCIES = qt5base qt5script
 
+# qt5 needs c++11 (since qt-5.7)
+ifeq ($(BR2_PACKAGE_QT5_VERSION_LATEST),y)
+GRANTLEE_CONF_OPTS += -DCMAKE_CXX_FLAGS="$(TARGET_CXXFLAGS) -std=c++11"
+endif
+
 $(eval $(cmake-package))