Support GnuTLS as an alternative crypto backend
This turns the -Dgcrypt
build time option into a tri-state option,
which enables user to choose which cryptographic library to link with.
It currently supports libgcrypt (libgcrypt
) and GnuTLS (gnutls
);
for the latter, a couple of legacy algorithms are disabled, namely
RIPEMD160 and PBES1-DES-SHA1 though it will be added in GnuTLS 3.8.5
for compatibility.