Berkeley DB XML Reference Guide: FreeBSD

I can't run Berkeley DB XML on a FreeBSD 5.4 machine.
On some installations of FreeBSD 5.4, you may see this runtime error:
```
Fatal error 'Spinlock called when not threaded.' at line 87 in file /usr/src/lib/libpthread/thread/thr_spinlock.c (errno = 0)
```
If this error is seen, it is necessary to create an /etc/libmap.conf file to map libc_r to libpthread. See "man 4 libmap.conf" for details on how to do this.