Fix regressions caused by symbol renaming changes.

Fix regressions caused by symbol renaming changes.

A bug in dxcommon was causing VPATH builds to continue to apply symbol
renaming to all gnulib sources.  Fixing this revealed that dependency
tracking was broken for the non-renamed objects (distcheck noticed that
the dependency products were not being cleaned).

To fix dependency tracking Automake needs to be aware of all the source
files going into the statically-linked version of the library.

Unfortunately, Automake complains if we just add the same sources to a
non-libtool library, even though there is no real conflict since only
one will actually be built.  The issue can be worked around by using
Automake's object renaming facilities, which complicates things slightly
but is straightforward enough to implement.