backend/Makefile was treating errcodes.h as a header always generated
during build, but actually it's a header provided in tarballs. Hence,
must use the absolute-symlink recipe, not the relative-symlink one.
Per bug #6072 from Hartmut Raschick.
$(LN_S) "$$prereqdir/$(notdir $<)" .
$(top_builddir)/src/include/utils/errcodes.h: utils/errcodes.h
- cd '$(dir $@)' && rm -f $(notdir $@) && \
- $(LN_S) "../../../$(subdir)/utils/errcodes.h" .
+ prereqdir=`cd '$(dir $<)' >/dev/null && pwd` && \
+ cd '$(dir $@)' && rm -f $(notdir $@) && \
+ $(LN_S) "$$prereqdir/$(notdir $<)" .
$(top_builddir)/src/include/utils/fmgroids.h: utils/fmgroids.h
prereqdir=`cd '$(dir $<)' >/dev/null && pwd` && \