Use autoconf, not OPENSSL_VERSION_NUMBER, to detect SSL_CIPHER_find

Repairs build with libressl

configure.ac

@@ -639,6 +639,7 @@ AC_CHECK_FUNCS([ \
 		SSL_get_server_random \
                 SSL_get_client_ciphers \
                 SSL_get_client_random \
+		SSL_CIPHER_find \
 	       ])
 LIBS="$save_LIBS"
 LDFLAGS="$save_LDFLAGS"

src/common/tortls.c

@@ -1487,7 +1487,7 @@ static int
 find_cipher_by_id(const SSL *ssl, const SSL_METHOD *m, uint16_t cipher)
 {
   const SSL_CIPHER *c;
-#if OPENSSL_VERSION_NUMBER >= OPENSSL_V_SERIES(1,0,2)
+#ifdef HAVE_SSL_CIPHER_FIND
   {
     unsigned char cipherid[3];
     tor_assert(ssl);