Adjustment to symbols_unix.map

I haven’t built master for some time, so this is a bit late.

To build on FreeBSD I need to add the following change, I don’t expect that would cause any issues on other platforms.

+++ b/source/creator/symbols_unix.map
@@ -39,6 +39,9 @@ global:
   realpath;
   sched_*;
   valloc;
+  /* needed on FreeBSD */
+  __progname;
+  environ;
 local:
   *;
 };

Does adding this patch cause issues for anyone?