Gets VPATH builds working again. The problem was that apr.h is generated

by autoconf and then placed in the builddir, not the srcdir (which we
didn't notice until we tried to do VPATH). When cpp couldn't find apr.h
we would decide not to build mod_so, which is kinda bad.

Now we include both paths when we test for APR_HAS_DSO and everyone is happy.


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@91537 13f79535-47bb-0310-9956-ffa450edef68