Silence warning:

oob_tcp_connection.c: In function 'mca_oob_tcp_peer_accept':
oob_tcp_connection.c:725:9: warning: variable 'cmpval' set but not used [-Wunused-but-set-variable]

Refs #3696
Silence warnings:

osc_pt2pt_data_move.c: In function 'ompi_osc_pt2pt_sendreq_recv_accum_long_cb':
osc_pt2pt_data_move.c:643:9: warning: variable 'ret' set but not used [-Wunused-but-set-variable]
osc_rdma_data_move.c: In function 'ompi_osc_rdma_control_send_cb':
osc_rdma_data_move.c:1312:37: warning: variable 'header' set but not used [-Wunused-but-set-variable]