allow to build on FreeBSD

This commit makes possible to compile pacemaker on FreeBSD systems (at least 9.1), assuming all prerequisites satisfied (libqb and corosync are "alien" to FreeBSD so should be built manually).
Tested configurations: FreeBSD 9.1 (amd64, i386), Ubuntu 13.04 (i686).

N.B. Nonetheless pacemaker does not function properly yet - small investigation showed that pacemaker requires /dev/shm to be present in system (libqd does, as QB_IPC_SHM is hardcoded in several places of pacemaker).
Mounting tmpfs did not give acceptable result (error: mainloop_add_ipc_server:      Could not start pacemakerd IPC server: Operation not supported (-45)), also changing IPC type to socket was unsuccessful.