Fixed a longstanding bug in configure.ac
which began to cause builds to fail with recent
autoconf.
Fixed a problem in test/CmakeLists.txt that caused
current builds to fail on Msys2 Mingw64. Had been
working for many months.
Updated the error report (for zlib, zstd) when
decompression exceeds a heuristic. Now reports
the compressed-len and the uncompressed-len.