Support for "pshared" POSIX semaphores

[Jason Thorpe <thorpej%me.com@localhost>]

-port-arm +tech-kern

> On Jan 24, 2019, at 5:58 AM, Jared McNeill <jmcneill%invisible.ca@localhost> wrote:
> 
> The tab crashes are related to http://gnats.netbsd.org/53273, which can be worked around by setting the autostart properties to false. The other crashes are not related, feel free to debug and fix them!

I’ve added support for “pshared” POSIX semaphores … it was beyond simply “broken” as described in lib/53273; there’s no way it could have ever worked.

My approach avoids breaking the client ABI, by ensuring that identifiers the kernel vends for pshared semaphores have a specific format, that works in both 32-bit (native or on 64-bit in compat) and 64-bit systems.  These specially-formatted IDs are substituted for the pointer to the user land semaphore structure in the pshared case; pshared semaphores don’t have any user land state.

Patch is here: https://patch-diff.githubusercontent.com/raw/thorpej/netbsd-src/pull/5.diff

I added a unit test for them, that (duh :-) passes.  I’ll try to test it w/ firefox52 on my Pinebook tomorrow.

-- thorpej