recognise new cygwin moniker reported by config.guess
TargetPlatform=i386-unknown-openbsd;;
i[[3456]]86-*-solaris2*)
TargetPlatform=i386-unknown-solaris2;;
TargetPlatform=i386-unknown-openbsd;;
i[[3456]]86-*-solaris2*)
TargetPlatform=i386-unknown-solaris2;;
-i[[3456]]86-*-cygwin32*)
exeext='.exe'
TargetPlatform=i386-unknown-cygwin32;;
i[[3456]]86-*-mingw32*)
exeext='.exe'
TargetPlatform=i386-unknown-cygwin32;;
i[[3456]]86-*-mingw32*)