Allow G3 re-write of zlib.h include

See cl/848244014 for motivation. Skia's Bazel build of zlib is updated
to export the zlib include directory. Bazel exports `hdrs` with
`-iquote` causing `<zlib.h>` style includes to not find the header.

Change-Id: I236b69ff5fe1eddae4be62f650012974a88a5821
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/1140756
Reviewed-by: Kaylee Lubick <kjlubick@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>