What's the best way to get flex and bison on Windows?

Hello,

On cfbot.cputube.org, we keep seeing random failures on appveyor (the
CI provider it uses for Windows) in this step:

- appveyor-retry cinst winflexbison

"cinst" is the apt/yum/pkg-like tool from the Chocolatey package
system, but unfortunately its repository is frequently unavailable.
"appveyor-retry" was added to cfbot by a pull request from David
Fettter (thanks!) and that reduced the rate of bogus failures quite a
lot by retrying 3 times, but I'm still seeing a sea of red from time
to time so I'd like to find a another source for those tools.

Here's the full set of software that is already installed on the
Windows build images:

https://www.appveyor.com/docs/windows-images-software/

You can see MinGW, MSYS and Cygwin there, and I suspect that one of
those is the answer, but I'm not familiar with them or what else might
be available to install popular F/OSS bits and pieces on that
operating system, because I really only know how to Unix. Maybe flex
and bison are already installed somewhere or easily installable with a
shell command? Would someone who knows about development on Windows
like to make a recommendation, or perhaps provide a tweaked version of
the attached patch[1]?

Thanks,

[1] Instructions: apply to the PG source, push to a public github
branch (or gitlab, kiln, ...), log into appveyor.com with your github
(or ...) account, add the project, watch it build and test.