non-openssl: only check for openssl ecdh in openssl builds
non-openssl: only check for openssl ecdh in openssl builds

See also
https://github.com/warmcat/libwebsockets/issues/559

Signed-off-by: Karl Palsson <cf2921c53fd940e0bab438c671bbd1b17f30b86b@etactica.com>

sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets,sartura/libwebsockets