Fix t/apr-ext failures when building without optimization.

APLOG_USE_MODULE() in modperl_apache_includes.h expands to a reference to perl_module, which is optimized away by -O2 when it's not used, but -O0 keeps it.

Patch by Niko Tyni. See also https://bugs.debian.org/756989.

git-svn-id: https://svn.apache.org/repos/asf/perl/modperl/trunk@1617722 13f79535-47bb-0310-9956-ffa450edef68
Simplify the avoidance of perl_module in places where it isn't (really) defined

Revision 1617722 pointed out an easier way to achieve what was done by revision 1502392. (Unfortunately, modperl_dummy.c is currently still required for the three other symbols that it provides, added by revision 1538006.)

git-svn-id: https://svn.apache.org/repos/asf/perl/modperl/trunk@1617727 13f79535-47bb-0310-9956-ffa450edef68