We previously needed to have empty targets because AM couldn't handle
having an AM_CONDITIONAL was targets in the "if" statement but not in the
"else". :-(
That now appears as an old automake bug that has been fixed,
so cleanup some Makefile.am
Thanks Jeff for the pointer.
Signed-off-by: Gilles Gouaillardet <gilles@rist.or.jp>
(cherry picked from commit open-mpi/ompi@6e04b2a66a)