CYGWIN: warning on missing safe memzero() is printed

[carlo-bramini]

Bug report

Bug description:

Compiling on CYGWIN gives this message on the console:

warning: Your platform does not support any safe implementation of memzero -- consider a pull request!

However, CYGWIN provides explicit_bzero(), actually.
The Modules/_hacl/Lib_Memzero0.c already supports it, so, a tiny fix is required for just adding __CYGWIN__ to the list of supported platforms.

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• gh-148200: fix warning on missing safe memzero() on CYGWIN #148202