message: add the error message in config.m4 of postgresql
diff: @@ -284,6 +284,9 @@ if test "$PHP_SWOOLE" != "no"; then
  AC_DEFINE(SW_USE_POSTGRESQL, 1, [enable coroutine-postgresql support])
  PHP_ADD_LIBRARY(pq, 1, SWOOLE_SHARED_LIBADD)
  fi
  + if test -z "$PGSQL_INCLUDE"; then
  + AC_MSG_ERROR(Cannot find libpq-fe.h. Please confirm the libpq or specify correct PostgreSQL(libpq) installation path)
  + fi
  fi
  if test "$PHP_HTTP2" = "yes"; then
  