code tweaks for clean build on AIX

src/api/checkpoint.c

src/common/env.c

src/plugins/checkpoint/aix/checkpoint_aix.c

src/plugins/mpi/mvapich/mvapich.c

src/plugins/sched/wiki/msg.c

src/plugins/sched/wiki2/msg.c

src/plugins/switch/federation/federation.c

src/slurmctld/job_mgr.c