Added subdir-objs to automake options

    * configure.ac: Added subdir-objs to automake options
    * gcc_plugin/Makefile.in: Regenerated
    * mageec/Makefile.in: Regenerated
    * ml/C5/Makefile.in: Regenerated
    * ml/Makefile.in: Regenerated
    * testsuite/gcc_plugin.tests/Makefile.in: Regenerated