We build static libraries with "ar crs" or "ar cr". If the static library
already exists in the build directory, those commands will add new members and
replace existing members. They will not remove members present in the
existing library but not named on the "ar" command line. This matters when,
for example, you rerun ./configure in a way that removes a file from
$(LIBOBJS). libpgport carries the obsolete member until "make clean". Let's
fix that by issuing "rm -f" before running $(AR). I would back-patch this.
