problem building linuxthreads on RELENG_6

[Tor Egge]

> Please apply following patch to devel/linuxthreads:

While fixing compilation on recent RELENG_6, that patch is a minor regression
for those running older snapshots of FreeBSD 7.0-CURRENT.

Feel free to commit this patch or a modified version that doesn't include the
regression for older snapshots of FreeBSD 7.0-CURRENT.  Currently, I don't have
permission to contribute code to FreeBSD.

- Tor Egge