[zlib] Adjust the scan[2]==match[2] assert for CRC hashing

When using CRC hashing, that assert doesn't hold, but a weaker variant
does.

Also disallow compiling with FASTEST defined, because I don't think
that longest_match variant would be safe with CRC hashing. It doesn't
guarantee that the fourth of the hashed bytes will be compared.

Bug: 1113596
Change-Id: I20ede29835b9c6b4bdc09fc1836864ffa2b10a97
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2401023


Commit-Queue: Hans Wennborg <hans@chromium.org>
Reviewed-by: Adenilson Cavalcanti <cavalcantii@chromium.org>
Cr-Commit-Position: refs/heads/master@{#805690}
GitOrigin-RevId: 6d189bdd1c456fe0db3042b1ef3507ee96a0ff15