pcp

Cleanup library build turds after recent oscillation on the
libpcp_pmcd.{so,dll,a} front.

If a build area has been used before those changes you still
have a libpcp_pmcd.so even on Linux, make clean does not remove
it, and make creates libpcp_pmcd.a. Then pmcd is incorrectly
linked with libpcp_pmcd.so. This fixes that corner case.