autotest/cpp: fix MSVC build in RelWithDebInfo and unity build

Author: rouault

autotest/cpp/CMakeLists.txt

@@ -111,6 +111,9 @@ target_link_libraries(gdal_unit_test PRIVATE $<TARGET_NAME:${GDAL_LIB_TARGET_NAM
 if(NOT MSVC AND CMAKE_THREAD_LIBS_INIT)
     target_link_libraries(gdal_unit_test PRIVATE ${CMAKE_THREAD_LIBS_INIT})
 endif()
+if (MSVC)
+   target_compile_options(gdal_unit_test PRIVATE "/bigobj")
+endif()
 gdal_standard_includes(gdal_unit_test)
 target_compile_options(gdal_unit_test PRIVATE ${GDAL_CXX_WARNING_FLAGS})
 target_compile_definitions(gdal_unit_test PRIVATE -DGDAL_TEST_ROOT_DIR="${GDAL_ROOT_TEST_DIR}")