Extracted private GetTimeZone() to public wxGetTimeZone() function.

Created new wx/time.h header for this function, more time-related functions
will be added to it later.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@69836 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

src/common/datetimefmt.cpp

@@ -57,6 +57,7 @@
 #endif
 
 #include "wx/datetime.h"
+#include "wx/time.h"
 
 // ============================================================================
 // implementation of wxDateTime
@@ -68,8 +69,6 @@
 
 extern void InitTm(struct tm& tm);
 
-extern int GetTimeZone();
-
 extern wxString CallStrftime(const wxString& format, const tm* tm);
 
 // ----------------------------------------------------------------------------
@@ -329,7 +328,7 @@ wxString wxDateTime::Format(const wxString& formatp, const TimeZone& tz) const
         // use strftime()
         struct tm tmstruct;
         struct tm *tm;
-        if ( tz.GetOffset() == -GetTimeZone() )
+        if ( tz.GetOffset() == -wxGetTimeZone() )
         {
             // we are working with local time
             tm = wxLocaltime_r(&time, &tmstruct);