Compile failures in 29 of 30 MTT builds last night: C++ bindings

[jsquyres]

Cisco shows compile failures in 29 out of 30 builds on master last night https://mtt.open-mpi.org/index.php?do_redir=2325.

The problem appears to be when compiling the C++ bindings (i.e., when you specify --enable-mpi-cxx) -- there's some kind of implicit casting going on that is fine in C, but not in C++:

make[2]: Entering directory `/home/jsquyres/git/o2/ompi/mpi/cxx'
  CXX      intercepts.lo
In file included from ../../../opal/include/opal/sys/atomic.h:615:0,
                 from ../../../opal/class/opal_object.h:124,
                 from ../../../ompi/errhandler/errhandler.h:32,
                 from intercepts.cc:27:
../../../ompi/request/request.h: In function 'int ompi_request_complete(ompi_request_t*, bool)':
../../../opal/include/opal/sys/atomic_impl.h:272:105: error: invalid conversion from 'void*' to 'ompi_wait_sync_t*' [-fpermissive]
 tr(addr, value) (void *) opal_atomic_swap_64((int64_t *) addr, (int64_t) value)

../../../opal/threads/wait_sync.h:33:41: note: in expansion of macro 'opal_atomic_swap_ptr'
 #define OPAL_ATOMIC_SWP_PTR(a,b)        opal_atomic_swap_ptr(a,b)
                                         ^
../../../ompi/request/request.h:416:38: note: in expansion of macro 'OPAL_ATOMIC_SWP_PTR'
         ompi_wait_sync_t *tmp_sync = OPAL_ATOMIC_SWP_PTR(&request->req_complete
                                      ^
make[2]: *** [intercepts.lo] Error 1