Fix flags in FormatMessage, Wvarargs warning fix

MinGW has been giving a warning about 'err is not last named argument' for the line '''va_start ( arg_ptr, err );'''; C standard says that va_start should use the last named argument with '''va_start'''. When going to fix this, I noticed the wrong flags have been supplied to FormatMessage, the '''FORMAT_MESSAGE_ARGUMENT_ARRAY''' flag is not supposed to be used with a '''va_list''' structure like it was in the code. After looking at the other places in OCE that use '''_osd_wnt_set_error''' and reading that using '''FORMAT_MESSAGE_FROM_SYSTEM''' shouldn't really be used with the optional argument list unless you're sure of the exact error and what that error message requires in terms of optional inserts, I figured I'd just neuter this function and leave out the optional arguments entirely.

src/OSD/OSD_FileNode.cxx

@@ -945,16 +945,13 @@ void _osd_wnt_set_error ( OSD_Error& err, OSD_WhoAmI who, ... ) {
 
  DWORD              errCode;
  Standard_Character buffer[ 2048 ];
- va_list            arg_ptr;
-
- va_start ( arg_ptr, err );
 
  errCode = GetLastError ();
 
  if (  !FormatMessage (
-         FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_ARGUMENT_ARRAY,
+         FORMAT_MESSAGE_FROM_SYSTEM | FORMAT_MESSAGE_IGNORE_INSERTS,
          0, errCode, MAKELANGID( LANG_NEUTRAL, SUBLANG_NEUTRAL ),
-         buffer, 2048, &arg_ptr
+         buffer, 2048, NULL
         )
  ) {
 
@@ -965,8 +962,6 @@ void _osd_wnt_set_error ( OSD_Error& err, OSD_WhoAmI who, ... ) {
 
  err.SetValue ( errCode, who, buffer );
 
- va_end ( arg_ptr );
-
 }  // end _set_error