Add OPENSSL_NO_ECDH guards

Reviewed-by: Emilia Käsper <emilia@openssl.org>
Add missing OPENSSL_NO_EC guards

Reviewed-by: Emilia Käsper <emilia@openssl.org>
Rename gost2814789t.c to gost2814789test.c. The old name caused problems
for dummytest if gost is compiled out, since the name of the test is not
standard (dummytest segfaults). Also the old name caused problems for git
because the executable was not in the .gitignore file

Reviewed-by: Emilia Käsper <emilia@openssl.org>
Add more meaningful OPENSSL_NO_ECDH error message for suite b mode

Reviewed-by: Emilia Käsper <emilia@openssl.org>