compilation fix for old SDK headers (such as shipped with VC6)

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@37629 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/msw/display.cpp

@@ -58,6 +58,19 @@
 
 #ifndef __WXWINCE__
     #include <multimon.h>
+
+    // HMONITOR can be declared either in new enough windef.h or in multimon.h
+    // itself if _WIN32_WINNT < 0x0500, but the trouble is that we set
+    // _WIN32_WINNT to maximal possible value ourselves in wx/msw/wrapwin.h so
+    // that multimon.h doesn't define it but with old headers, neither does
+    // windef.h, in spite of _WIN32_WINNT value. Even more unfortunately, we
+    // can't directly test whether HMONITOR is defined or not in windef.h as
+    // it's not a macro but a typedef, so we test for an unrelated symbol which
+    // is only defined in winuser.h if WINVER >= 0x0500
+    #if !defined(HMONITOR_DECLARED) && !defined(MNS_NOCHECK)
+        DECLARE_HANDLE(HMONITOR);
+        #define HMONITOR_DECLARED
+    #endif
 #endif // !__WXWINCE__
 
 #ifdef _MSC_VER