OpenBSD doesn't have RLIMIT_AS

[Coleman McFarland]

I pulled got a new compiler error with oils-for-unix-0.22.0. It seems to have been introduced in 0.22.0

_gen/bin/oils_for_unix.mycpp.cc:17576:12: error: use of undeclared identifier 'RLIMIT_AS'
    what = RLIMIT_AS;

OpenBSD doesn't have RLIMIT_AS. This manpage search site matches what I see for man getrlimit.

https://man.ifconfig.se/getrlimit.2

The fact that it's missing is listed as a bug :) so maybe someday you'll be able to get rid of this ifdef.

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For what it's worth, FreeBSD seems to support it. I don't have a FreeBSD system to test on, though.