Upgrade zlib to 1.2.12, from 1.2.11

Current release:
zlib 1.2.12
March 27, 2022

Version 1.2.12 has these key improvements over 1.2.11:
Fix a deflate bug when using the Z_FIXED strategy that can result in out-of-bound accesses.
Fix a deflate bug when the window is full in deflate_stored().
Speed up CRC-32 computations by a factor of 1.5 to 3.
Use the hardware CRC-32 instruction on ARMv8 processors.
Speed up crc32_combine() with powers of x tables.
Add crc32_combine_gen() and crc32_combine_op() for fast combines.