Fix the CXXDEBUG/OpenMesh issue

Scripts/developer_scripts/autotest_cgal

@@ -510,7 +510,9 @@ build_cgal_on_host()
 
         cat >> "${CGAL_BINARY_DIR}/localbuildscript" <<EOF
 CGAL_BINARY_DIR='${CGAL_BINARY_DIR}';
-CMAKE_GENERATOR='${CMAKE_GENERATOR}';
+if [ -z "\$CMAKE_GENERATOR" ]; then
+  CMAKE_GENERATOR='${CMAKE_GENERATOR}';
+fi
 MAKE_CMD='${MAKE_CMD}';
 CGAL_REFERENCE_CACHE_DIR='${CGAL_REFERENCE_CACHE_DIR}';
 export CMAKE_GENERATOR;
@@ -608,7 +610,9 @@ else
 fi
 CGAL_TEST_HOST='${HOST}';
 CGAL_TEST_PLATFORM='${PLATFORM}';
-CMAKE_GENERATOR='${CMAKE_GENERATOR}'
+if [ -z "\$CMAKE_GENERATOR" ]; then
+  CMAKE_GENERATOR='${CMAKE_GENERATOR}';
+fi
 MAKE_CMD='${MAKE_CMD}'
 export CGAL_TESTER CGAL_TESTER_NAME CGAL_TESTER_ADDRESS;
 export CGAL_DIR;