Test for wcsftime() in configure as it's not available everywhere.

Contrary to the comment in wx/wxcrtbase.h, wcsftime() doesn't seem to be
available under quite all the systems, notably it doesn't seem to be present
in OpenBSD at all, even in the very latest version.

Add a configure test for this function and fall back to our own implementation
if the system doesn't have it.

Closes #12766.

git-svn-id: https://svn.wxwidgets.org/svn/wx/wxWidgets/trunk@66446 c3d73ce0-8a6f-49c7-b76d-6d57e0e08775

include/wx/wxcrtbase.h

@@ -664,8 +664,11 @@ WXDLLIMPEXP_BASE wchar_t * wxCRT_GetenvW(const wchar_t *name);
     _xpg5_wcsftime(wchar_t *, size_t, const wchar_t *, const struct tm * );
     #define wxCRT_StrftimeW _xpg5_wcsftime
 #else
-    #ifndef __WXPALMOS__
-        // assume it's always available, this does seem to be the case for now
+    // Assume it's always available under non-Unix systems with the exception
+    // of Palm OS, this does seem to be the case for now. And under Unix we
+    // trust configure to detect it (except for SGI special case above).
+    #if defined(HAVE_WCSFTIME) || \
+        !(defined(__UNIX__) || defined(__WXPALMOS__))
         #define wxCRT_StrftimeW  wcsftime
     #endif /* ! __WXPALMOS__ */
 #endif