Fix build error with OpenSSL < 1.0.2

src/shrpx_ssl.cc

@@ -490,6 +490,7 @@ namespace {
 constexpr unsigned int TLS_EXT_SIGNED_CERTIFICATE_TIMESTAMP = 18;
 } // namespace
 
+#if !LIBRESSL_IN_USE && OPENSSL_VERSION_NUMBER >= 0x10002000L
 namespace {
 int sct_add_cb(SSL *ssl, unsigned int ext_type, const unsigned char **out,
                size_t *outlen, int *al, void *add_arg) {
@@ -522,6 +523,7 @@ int sct_parse_cb(SSL *ssl, unsigned int ext_type, const unsigned char *in,
   return 1;
 }
 } // namespace
+#endif // !LIBRESSL_IN_USE && OPENSSL_VERSION_NUMBER >= 0x10002000L
 
 struct TLSProtocol {
   StringRef name;