Keep all comments in the user-facing mpi.h.in as "old style" C
comments: /* */. This gives us maximum portability, just on the off
chance that a user's C compiler does not support //-style comments.
Signed-off-by: Jeff Squyres <jsquyres@cisco.com>
(cherry picked from commit d522c270373264aff0a7a2066bc3163b09e9a94b)