Dereference INTDIR in serf.mak.
Dereference INTDIR in serf.mak.

* serf.mak
  (ALL, INTDIR, CHECK, STATIC_LIB): Use $(INTDIR) instead of INTDIR.

Patch by dpb at corrigendum.ru.

jandre/serf,jandre/serf,jandre/serf,jandre/serf