[zlib] Enable file descriptor operations on Fuchsia

This enables APIs that take file descriptor arguments on Fuchsia.
Previously, these were only enabled on POSIX platforms. Since Fuchsia
also uses file descriptors, these APIs are now also enabled on
Fuchsia.

Bug: 1290560
Change-Id: I282e712dca4b57a0551df0266f85b025556ffc71
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/3479958


Reviewed-by: Adam Langley <agl@chromium.org>
Commit-Queue: Fabrice de Gans <fdegans@chromium.org>
Cr-Commit-Position: refs/heads/main@{#973781}
NOKEYCHECK=True
GitOrigin-RevId: 0936966bdc62b5d714ea68e4efb5324853217c0a