Apply the Tru64 patch from Tim Mooney <mooney@dogbert.cc.ndsu.NoDak.edu>

His comments are:

1) Changes all references for `True64' to be `Tru64', which is the correct
spelling for the OS name.

2) Makes `alpha-cc' be the same as `alpha164-cc', and adds an `alphaold-cc'
entry that is the same as the previous `alpha-cc'.  The reason is that most
people these days are using the newer compiler, so it should be the default.

3) Adds a bit of commentary to Configure, regarding the name changes of
the OS over the years, so it's not so confusing to people that haven't been
with the OS for a while.

4) Adds an `alpha-cc-rpath' target (which is *not* selected automatically
by Configure under any circumstance) that builds an RPATH into the
shared libraries.  This is explained in the comment in Configure.  It's
very very useful for people that want it, and people that don't want it
just shouldn't choose that target.

5) Adds the `-pthread' flag as the best way to get POSIX thread support
from the newer compiler.

6) ...