routine PREFIX-aware and compatible with our install(1). As a bonus,
it would install prefixed binaries to avoid potential clash with other
gzip and gunzip implementations.
compression and decompression.
WWW: https://github.com/ebiggers/libdeflate
Because GitHub releases (tarballs) are not fetched with correct modification
time, set TIMESTAMP to 1501364283 which corresponds to commit 3d96a83 tagged
as this release.
