tests/scripts/curves.pl tests the library with a single curve enabled.
This uses the legacy ECDH context and the default ECDH implementation.
For Curve25519, there is an alternative implementation, which is
Everest. Test this. This also tests the new ECDH context, which
Everest requires.
Signed-off-by: Gilles Peskine <Gilles.Peskine@arm.com>