Fix invalid read in zlib

adler32_vec on arm reads past the end of its buffer when checksumming the decompressed data. This PR fixes that. The problem was detected with valgrind.

I've checked the bundled copies of zlib in other parts of mer and nemo, and those are unaffected because they don't have the adler32_vec patch.

The huge size of this PR is mostly because a huge patch got moved from rpm/ to be a git commit. No code was changed in 3aced48.