make: add tmalloc lib dep in tcmalloc guard

Fixes --without-tcmalloc on boxes without libtcmalloc.

Signed-off-by: Noah Watkins <noahwatkins@gmail.com>
Merge pull request #594 from ceph/fix-no-tcmalloc-build

make: add tmalloc lib dep in tcmalloc guard

Reviewed-by: Sage Weil <sage@inktank.com>