Add IPC information for Darwin

[jamesodhunt]

Find a way to support the following on Darwin:

• --message-queues
• --semaphores
• --shared-memory

The fundamental problem is that Darwin's shmctl(2) doesn't support the IPC_INFO command. However, presumably there is some equivalent using the Mach API.

[jamesodhunt]

From https://opensource.apple.com/source/xnu/xnu-792.24.17/bsd/sys/ipcs.h.auto.html:

/*
 * NOTE: Internal ipcs.h header; all interfaces are private; if you want this
 * same information from your own program, popen(3) the ipcs(2) command and
 * parse its output, or your program may not work on future OS releases.
 */

Ugh 😭