security/ncrack: fix build on -CURRENT

This port seems to have been affected by the recent FORTIFY_SOURCE
update on -CURRENT. The error message was:

In file included from strlcpy.c:21:
In file included from ./includes.h:190:
In file included from ./entropy.h:30:
In file included from ./buffer.h:28:
In file included from ./sshbuf.h:29:
In file included from /usr/local/include/openssl/bn.h:26:
In file included from /usr/local/include/openssl/crypto.h:25:
In file included from /usr/include/stdlib.h:73:
/usr/include/ssp/stdlib.h:41:33: error: static declaration of

            '_ssh_compat_realpath' follows non-static declaration
41 | __ssp_redirect_raw_impl(char *, realpath, realpath,
   |                                 ^

./openbsd-compat.h:98:7: note: previous declaration is here

98 | char *realpath(const char *path, char *resolved);
   |       ^

./openbsd-compat.h:95:26: note: expanded from macro 'realpath'

95 | #  define realpath(x, y) _ssh_compat_realpath(x, y)
   |                          ^

2 errors generated.