Problems configuring 21.4.12 on Cygwin

Hi! I see the following at orkplace: % sh configure \ --prefix=${PREFIX} \ --site-includes=/usr/local/include \ --site-libraries=/usr/local/lib \ --x-includes=/usr/X11R6/include \ --x-libraries=/usr/X11R6/lib \ --with-dialogs=athena \ --with-scrollbars=no \ --with-toolbars=no \ --with-widgets=athena \ --use-union-type \ --with-mule \ --pdump [...] checking for X... libraries /usr/X11R6/lib, headers /usr/X11R6/include checking for dnet_ntoa in -ldnet... no checking for dnet_ntoa in -ldnet_stub... no checking for gethostbyname... yes checking for connect... yes checking for remove... yes checking for shmat... no checking for shmat in -lipc... no checking for IceConnectionNumber in -lICE... yes checking for X defines extracted by xmkmf checking for X11/Intrinsic.h... no configure: error: Unable to find X11 header files. % ls -l /usr/X11R6/include/X11/Intrinsic.h -rwxrwxrwx 1 Administ 65535 73241 Jan 21 2002 /usr/X11R6/include/X11/Intrinsic.h Is there a way to make configure "see" the header? Thanks, norbert.