This is helpful in the work for #3694: ensure that many places that
eventually end up in configure don't overly-pollute the global shell
variable space (because debugging accidental shell variable pollution
can be a real pain).
Refs trac:3694
This commit was SVN r29830.
The following Trac tickets were found above:
Ticket 3694 --> https://svn.open-mpi.org/trac/ompi/ticket/3694