Hi,
The error you got compiling is because of Freebsd 4.11 being ancient and our code not caring about that.
There's a workaround shown below courtesy of xchat logs and Rob.
Nonetheless, that doesn't explain your actual issue, can you show us the output of /os modlist please.
Nov 12 17:20:09 <Rob> ok, first up, gmake distclean
Nov 12 17:20:45 <Rob> let it do stuff
Nov 12 17:21:16 <Rob> ok, now do ./Config
Nov 12 17:21:18 <Rob> let it do stuff
Nov 12 17:23:35 <Rob> ok, now cd into the include directory
Nov 12 17:23:40 <Rob> and edit sysconf.h
Nov 12 17:23:51 <Rob> look for #define HAVE_BACKTRACE 1
Nov 12 17:25:12 <Rob> ok, delete that line
Nov 12 17:25:41 <Rob> kk, save it, and go back into the anope dir
Nov 12 17:25:44 <Rob> then do: gmake
Nov 12 17:27:53 <Rob> once that's done, you should be able to gmake install