primarily of pointless $FreeBSD$ tags), sync most files in HEAD with
those in the ZLIB branch. This minimizes the differences between
HEAD and ZLIB and should simplify future imports.
After this, there are only three files with local modifications
(gzio.c, minigzip.c, and zconf.h) and two non-vendor files
(Makefile, zopen.c). The rest exactly match the vendor distribution.
PR: i386/76294
MFC after: 2 weeks
