9d36bf891b
This reduces duplication: we only need to distinguish between Windows
and Unix in one place.
The previous code was inconsistent about using either the `platforms`
option, or the `host_machine`. Following the logic described in
commit 94379377 "lavapipe: build "Windows" check should use the host machine, not the `platforms` option.",
I've assumed that checking the host machine is the more-correct version
and used that.
Signed-off-by: Simon McVittie <smcv@collabora.com>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/37576>