Allow compiling without RSA or DH

Only library and programs now, need to check test suites later.
diff --git a/library/ssl_srv.c b/library/ssl_srv.c
index ff914e5..ce45898 100644
--- a/library/ssl_srv.c
+++ b/library/ssl_srv.c
@@ -2144,7 +2144,8 @@
 #endif /* POLARSSL_KEY_EXCHANGE_DHE_RSA_ENABLED ||
           POLARSSL_KEY_EXCHANGE_DHE_PSK_ENABLED */
 
-#if defined(POLARSSL_KEY_EXCHANGE_ECDHE_RSA_ENABLED)
+#if defined(POLARSSL_KEY_EXCHANGE_ECDHE_RSA_ENABLED) ||                     \
+    defined(POLARSSL_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED)
 static int ssl_parse_client_ecdh_public( ssl_context *ssl )
 {
     int ret = POLARSSL_ERR_SSL_FEATURE_UNAVAILABLE;
@@ -2173,7 +2174,8 @@
 
     return( ret );
 }
-#endif /* POLARSSL_KEY_EXCHANGE_ECDHE_RSA_ENABLED */
+#endif /* POLARSSL_KEY_EXCHANGE_ECDHE_RSA_ENABLED ||
+          POLARSSL_KEY_EXCHANGE_ECDHE_ECDSA_ENABLED */
 
 #if defined(POLARSSL_KEY_EXCHANGE_RSA_ENABLED)
 static int ssl_parse_encrypted_pms_secret( ssl_context *ssl )