Repair for non-ECC OpenSSL.

Ifdef out the ECC parts when building with an OpenSSL that doesn't have
it.
diff --git a/sshd.c b/sshd.c
index 312dcd8..e1c767c 100644
--- a/sshd.c
+++ b/sshd.c
@@ -2570,7 +2570,9 @@
 	kex->kex[KEX_DH_GRP14_SHA1] = kexdh_server;
 	kex->kex[KEX_DH_GEX_SHA1] = kexgex_server;
 	kex->kex[KEX_DH_GEX_SHA256] = kexgex_server;
+# ifdef OPENSSL_HAS_ECC
 	kex->kex[KEX_ECDH_SHA2] = kexecdh_server;
+# endif
 #endif
 	kex->kex[KEX_C25519_SHA256] = kexc25519_server;
 	kex->server = 1;