Here's some followups for your suggestions, and a patch to make them so.

> It isn't very important, but perhaps it would make more sense to have
> it that way, in the same style that we have packages/Linux/RPM.
> It would also require that the current packages/Win32 stuff is moved
> into packages/Win32/mingw.

I made necessary changes (see attached .patch) to move the cygwin stuff
into the sub-directory. I did not make any changes for the mingw stuff.

> Ah, the root makefile is already polluted with some package-specific
> targets so I figure it is OK. Let's try to stay with the goal that
> any extra package-specific files are added in the their respective
> packages-directory though.

I took most of the cygwin stuff out of the root makefile (except for a
one-liner that calls down into the cygwin-specific makefile). If you'd
rather not even have that one-liner in there, please feel free to
remove it, but then also please update my cygwin-specific README to
match.

> BTW, a minor nitpick: "CygwinTmp = /tmp/curl-binary-build"
> wouldn't it be better to 1) use a local temporary path
> and 2) use the pid or something in the path to make it "unique"
> and thus enable two simultaneous builds...

I moved it to a sub-directory of <top_builddir>/packages/Win32/cygwin,
so as long as different "build-dirs" are used, simultaneous builds
should be OK now.

--Kevin