I met the problem as you describing. I find your patch file does not match the source code of mod_fastcgi.c in lighttpd-1.4.18. Such as:

these line is not exists in mod_fastcgi.c:

-                                       log_error_write(srv, __FILE__, __LINE__, "sb",
-                                    "send-file error: couldn't get stat_cache entry for:",

This make patch process fail, command info is:

patching file mod_fastcgi.c
Hunk #1 FAILED at 2530.
Hunk #2 FAILED at 59.
2 out of 2 hunks FAILED -- saving rejects to file mod_fastcgi.c.rej

Could you give me some advice? Thank your very much!

Robbin Fan