Fix WIN32 build for map_test.

stubs/common.h undefines the GetMessage macro introduced in windows.h
map_test however include stubs/common.h before windows.h is transitively
included. This hack force map_test.cc to include windows.h first, so we
have a chance to undefine the GetMessage macro.

src/google/protobuf/map_test.cc

@@ -28,6 +28,12 @@
 // (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
 // OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
 
+// A hack to include windows.h first, which ensures the GetMessage macro can
+// be undefined when we include <google/protobuf/stubs/common.h>
+#if defined(_WIN32)
+#include <windows.h>
+#endif  // _WIN32
+
 #include <algorithm>
 #include <google/protobuf/stubs/hash.h>
 #include <map>