into a single object module. This avoids client programs picking
up part of the allocation routines from mmalloc and part from libc,
which can lead to undefined behavior.
(CFILES): Add mm.c
(TARGETOBJS): Define to be either the individual objects or the
single combined object.
(TARGETLIB): Create the archive using TARGETOBJS.
* mm.c: New file that simply #includes the other source C files.
