Tweak apache/apr builds to support dsos on OS/390.

The OS/390 compile options are hard-coded because we need the
special DLL,EXPORTALL on *all* object files that are part of the
core so that dsos can reference symbols in the core.  (Of course,
we use the option on more object files than that, but it doesn't
seem to hurt anything.)

We hard-code the enablement of DSOs on OS/390 because the
library functions on OS/390 to manage explicit loading are not
portable, so there seems to be no use in probing for them.

Submitted by:	Greg Ames


git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@86098 13f79535-47bb-0310-9956-ffa450edef68