[zlib][build] Use relative path to reference zlib

Non-Chromium projects like Node.js ship zlib in non-standard paths.

Bug: 1422884
Change-Id: I00228b02f59d1a7244af05fa00e2fe7fc689e352
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/4322720


Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Commit-Queue: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Commit-Position: refs/heads/main@{#1115219}
NOKEYCHECK=True
GitOrigin-RevId: 2fda754a46a35ba06c4ce23b1f2cd1bfa60de951