…laris.

It turns out that `echo $PWD` isn't *quite* portable. The test assumes that
the shell will set the environment variable PWD to the current directory as
part of its startup. This is needed, because the implementation detail being
tested here is that the command is run with a *different* current directory
from the Raku code - ie there is a `chdir` happening as part of the command
invocation, without affecting the invokee.

Solaris (these days) uses ksh93, and *that* turns out to be wonderfully
special. If the current directory is `/` or `~`, then it *does* set PWD (to
the canonical path). Otherwise it leaves PWD unchanged.

I *guess* that this is because it has to figure out the name => (dev,ino)
mapping for these two paths anyway, and it's cheap to stat("."), so it
updates PWD if it happens to find that it knows the pathname corresponding
to "."'s (dev,ino), but doesn't do any extra work if it doesn't recognise
".". I don't find this documented anywhere.

AIX appears to use an older ksh, and that *is* updating PWD.
(That's all the vendor OSes I currently have access to, to test.)

So run `pwd` instead of relying on $PWD being set. I think that this will
also work even if the shell is a Bourne Shell, as I don't believe that
there's any *requirement* for the shell to set this variable.

So Zoffix Znet was correct to write

    Don't know how sanely portable that is...

in Jan 2018 in #375