sendmsg, recvmsg: moved MSG_CMSG_COMPAT definition to a header

sendmsg01.c and recvmsg01.c both define MSG_CMSG_COMPAT in a
similar way. Moved this definition to a new header file to reduce
code duplication.

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>
msg_common.h: corrected __sparc64__ definition

__sparc64__ is not defined by cpp. We should use
'__sparc__' and '__arch64__' instead.

Author: Jose E. Marchesi <jose.marchesi@oracle.com>

Signed-off-by: Stanislav Kholmanskikh <stanislav.kholmanskikh@oracle.com>