Try to fix a package build error that I cannot reproduce on my system.

Even though "poudriere testport" completed without error, I have received
a failure message from the build cluster. Since I cannot reproduce the
problem, I can only guess that it is caused by a symbolic link in the
share/nls directory that connects nls/C to nls/en_US.US-ASCII.

I had problems with the nls/C directory disappearing due to that link
before (it is deleted as empty when the last catalog file is deleted on
package deinstallation, but then missing when a new file is installed
into en_US.US-ASCII, which is just a symbolic link to C which does not
exist at that time anymore). I think this is a bug in "pkg" and have
opened a PR.

It is possible that the port will still fail to build in the cluster,
but without access to the work directory (or rather the stage directory)
of the build host I can only guess what's exactly going on.

IMHO there should not be any magic conenction between nls/en_US.US-ASCII
and nls/C, since this breaks assumptions made in pkg and in the qa check
performed by poudriere.

Approved by: antoine (implicit)