Fix building the mpmt MPM. The problem was that IfModule uses the name of

Fix building the mpmt MPM.  The problem was that IfModule uses the name of
the C file to determine if a module is present.  mpmt emulates three
different MPMs though.  If the default config file we have sane defaults
for each of the three MPMs that mpmt emulates.

To fix this, the build process creates a soft link to the original MPM name
during the configure process, and the build process actually compiles that
file, instead of the original mpmt.c.  This allow the mpmt MPM to work
just as well as mpmt_pthread.

git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@85798 13f79535-47bb-0310-9956-ffa450edef68