Extract setting WINVER/_WIN32_WINNT to a separate file

This will allow reusing it from other places.

Makefile.in

@@ -743,6 +743,7 @@ ALL_PORTS_BASE_HEADERS =  \
 	wx/msw/stackwalk.h \
 	wx/msw/stdpaths.h \
 	wx/msw/winundef.h \
+	wx/msw/winver.h \
 	wx/msw/wrapcctl.h \
 	wx/msw/wrapcdlg.h \
 	wx/msw/wrapwin.h \
@@ -2581,6 +2582,7 @@ COND_PLATFORM_WIN32_1_BASE_PLATFORM_HDR =  \
 	wx/msw/stackwalk.h \
 	wx/msw/stdpaths.h \
 	wx/msw/winundef.h \
+	wx/msw/winver.h \
 	wx/msw/wrapcctl.h \
 	wx/msw/wrapcdlg.h \
 	wx/msw/wrapwin.h \

build/bakefiles/files.bkl

@@ -169,6 +169,7 @@ IMPORTANT: please read docs/tech/tn0016.txt before modifying this file!
     wx/msw/stackwalk.h
     wx/msw/stdpaths.h
     wx/msw/winundef.h
+    wx/msw/winver.h
     wx/msw/wrapcctl.h
     wx/msw/wrapcdlg.h
     wx/msw/wrapwin.h

build/files

@@ -124,6 +124,7 @@ BASE_WIN32_HDR =
     wx/msw/stackwalk.h
     wx/msw/stdpaths.h
     wx/msw/winundef.h
+    wx/msw/winver.h
     wx/msw/wrapcctl.h
     wx/msw/wrapcdlg.h
     wx/msw/wrapwin.h

include/wx/msw/winver.h

@@ -0,0 +1,36 @@
+///////////////////////////////////////////////////////////////////////////////
+// Name:        wx/msw/winver.h
+// Purpose:     Define Windows version macros if they're not predefined.
+// Author:      Vadim Zeitlin
+// Created:     2017-01-13 (extracted from wx/msw/wrapwin.h)
+// Copyright:   (c) 2017 Vadim Zeitlin <vadim@wxwidgets.org>
+// Licence:     wxWindows licence
+///////////////////////////////////////////////////////////////////////////////
+
+#ifndef _WX_MSW_WINVER_H_
+#define _WX_MSW_WINVER_H_
+
+// Notice that this header must not include any other wx headers as it's
+// indirectly included from wx/defs.h itself when using gcc (via wx/platform.h,
+// then wx/compiler.h and wx/msw/gccpriv.h).
+
+// Define WINVER, _WIN32_WINNT and _WIN32_IE to the highest possible values
+// because we always check for the version of installed DLLs at runtime anyway
+// (see wxGetWinVersion() and wxApp::GetComCtl32Version()) unless the user
+// really doesn't want to use APIs only available on later OS versions and had
+// defined them to (presumably lower) values -- or, alternatively, wants to use
+// even higher version of the API which will become available later.
+
+#ifndef WINVER
+    #define WINVER 0x0603
+#endif
+
+#ifndef _WIN32_WINNT
+    #define _WIN32_WINNT 0x0603
+#endif
+
+#ifndef _WIN32_IE
+    #define _WIN32_IE 0x0700
+#endif
+
+#endif // _WX_MSW_WINVER_H_

include/wx/msw/wrapwin.h

@@ -12,6 +12,10 @@
 
 #include "wx/platform.h"
 
+// before including windows.h, define version macros at (currently) maximal
+// values because we do all our checks at run-time anyhow
+#include "wx/msw/winver.h"
+
 // strict type checking to detect conversion from HFOO to HBAR at compile-time
 #ifndef STRICT
     #define STRICT 1
@@ -24,25 +28,6 @@
 #endif // NOMINMAX
 
 
-// before including windows.h, define version macros at (currently) maximal
-// values because we do all our checks at run-time anyhow
-#ifndef WINVER
-    #define WINVER 0x0603
-#endif
-
-// define _WIN32_WINNT and _WIN32_IE to the highest possible values because we
-// always check for the version of installed DLLs at runtime anyway (see
-// wxGetWinVersion() and wxApp::GetComCtl32Version()) unless the user really
-// doesn't want to use APIs only available on later OS versions and had defined
-// them to (presumably lower) values
-#ifndef _WIN32_WINNT
-    #define _WIN32_WINNT 0x0603
-#endif
-
-#ifndef _WIN32_IE
-    #define _WIN32_IE 0x0700
-#endif
-
 // For IPv6 support, we must include winsock2.h before winsock.h, and
 // windows.h include winsock.h so do it before including it
 #if wxUSE_IPV6