* aclocal/canonical-target-name.m4: Use AC_CANONICAL_TARGET instead
of AC_CANONICAL_SYSTEM.
* aclocal/config-subdirs.m4: Use AS_MKDIR_P instead of
mkinstalldirs and mkdir.
* aclocal/target.m4: Obsolete RTEMS_OUTPUT_BUILD_SUBDIRS,
hack RTEMS_CONFIG_BUILD_SUBDIRS, introduce
_RTEMS_OUTPUT_BUILD_SUBDIRS.