This reverts commit d31634c358.
Laurent Thomas had a problem on one machine with the build_oai
way of checking for nettle.
The problem with the alternative solution of including nettle/bignum.h
is that it is very unclear.
The problem with nettle is that the file nettle/config.h does not
exist for version 2. It was introduced in version 3.
We want to support both versions, but there is an API incompatibility.
So we need an #if #else mechanism.
The file nettle/bignum.h is present in both versions 2 and 3 and it
includes nettle/version.h in the version 3.
So by including this file, we can check for the existence of
NETTLE_VERSION_MAJOR (that comes from nettle/config.h) in the
code.
But as you can see, the reasoning is way too complex.
So it's better to keep the check in cmake_targets/CMakeLists.txt.
As long as we support version 2 this will be the way to go.
It is possible to force a given version in specific non-generic
customized environments.
Cedric Roux
76574a1ac0