As a followup to #29053, in analogy to the work done for debian/fedora/arch/conda, we
add files build/pkgs/SPKG/distros/cygwin.txt to keep track of equivalent distribution packages

using these sources:

• https://github.com/sagemath/sage-windows/blob/master/cygwin-sage-build.list
• https://github.com/sagemath/sage-windows/blob/master/cygwin-sage-runtime.list
• https://trac.sagemath.org/wiki/Cygwin64Port

Follow-up: #29295 - Add GitHub CI workflow for cygwin

CC: @embray @dimpase @tscrim

Component: porting: Cygwin

Author: Erik Bray, Matthias Koeppe

Branch/Commit: 14f2967

Reviewer: Dima Pasechnik

Issue created by migration from https://trac.sagemath.org/ticket/29106