Cywin port notes  - John Belmonte <john@nanaon-sha.co.jp>
 
    (*) The Cygwin port is configured with UNIX=true.
 
    (*) Currently the Cygwin distribution does not come with yacc, so
    the YACC variable is set to empty string.  If you have yacc
    installed you may set YACC from your environment.
 
    (*) The build Jamfile was assuming that YACC is defined if UNIX
    is true.  (Note that besides CYGWIN, the BEOS definition also
    violates this assumption.)  This was corrected.
 
    (*) There is a subtle problem with the GenFile rule that occurs
    when the SUFEXE and system script suffix are different, as is the
    case with Cygwin. (Binaries use .exe but scripts have no suffix.)
    Although the Jambase docs on GenFile state that the image is to be
    "an executable built by the Main rule", it seems common to also
    use it with external programs and scripts.  (The build Jamfile
    itself does this when it calls the "yyacc" script.)  GenFile
    applies SUFEXE in all cases, so when used with a script on Cywin
    it will try to use <scriptname>.exe and fail.
 
"The Cygwin tools are ports of the popular GNU development tools and
utilities for Windows 95, 98, and NT. They function by using the
Cygwin library which provides a UNIX-like API on top of the Win32
API."   <http://sourceware.cygnus.com/cygwin/>