Explicitly define build type to add NDEBUG flag

debian/rules

@@ -8,6 +8,7 @@ override_dh_auto_configure:
 	dh_auto_configure -- \
 		-DCMAKE_INSTALL_RPATH_USE_LINK_PATH=ON \
 		-DCMAKE_INSTALL_RPATH=/usr/lib/$(DEB_HOST_MULTIARCH)/vcmi \
+		-DCMAKE_BUILD_TYPE=RelWithDebInfo \
 		-DBIN_DIR=games \
 		-DFORCE_BUNDLED_FL=OFF \
 		-DENABLE_TEST=0