mpi/longlong.h: fix missing macro parameter parentheses
* mpi/longlong.h [__alpha] (umul_ppmm): Add parentheses around used parameters. [__i370__] (sdiv_qrnnd): Ditto. [__mips__] (umul_ppmm): Ditto. [__vax__] (sdiv_qrnnd): Ditto.
Noticed issue after wrong results on mips64 with new mpi/ec code.
- Signed-off-by: Jussi Kivilinna <jussi.kivilinna@iki.fi>