problems with freebsd 4.5

[Marcello Silva Coutinho]

        when i try to compile nessus(1.09 or 1.10) in a freebsd4.5, I get
this error message:
gcc -g -O2 `./cflags` -c html_graph_output.c
html_graph_output.c:69: conflicting types for `strcasestr'
/usr/include/string.h:86: previous declaration of `strcasestr'
*** Error code 1

Stop in /tmp/nessus-install.50612/nessus-core/nessus.
*** Error code 1

Stop in /tmp/nessus-install.50612/nessus-core.
**** An error occured :/
Press any key to quit