hard-link locking & filesystems

[Jeff Dubrule]

When a compiler is insufficiently cool, libtool uses hard-link locking
to prevent the same file from being compiled in the same place.

It does this by waiting until:

ln /usr/bin/libtool whatever.lock

succeeds.

However, if libtool is installed on a different filesystem from where
the compile is proceeding (/usr vs /home, for example), this will
never succeed, and will sit there saying:

Waiting for bcfmail.o.lock to be removed
Waiting for bcfmail.o.lock to be removed
Waiting for bcfmail.o.lock to be removed
...

The hard-link-locking check in configure, naturally, does not catch
this problem.

Hard-link-locking, if we're to keep using it, should lock to a temp
file created in the same directory.

-jeff