Re: 'state_not_recoverable' is not a member of 'std::errc' on clang build (was: clang-13.0.1nb1 build from pkgsrc 2022Q2 fails on NetBSD-9.2_STABLE (2022-07-01))

[Robert Elz <kre%munnari.OZ.AU@localhost>]

    Date:        Fri, 22 Jul 2022 10:02:48 +0200
    From:        Hauke Fath <hf%spg.tu-darmstadt.de@localhost>
    Message-ID:  <20220722100248112297.35703c73%spg.tu-darmstadt.de@localhost>

  | Well, provided the (newer) kernel has backward compatibility, what 
  | determines the "system version" is really the system headers and 
  | libraries, not the kernel API. So one might want to look at 
  | /etc/release, instead of uname output...

That is all very true ... but /etc/release is kind of local, and is
a 150 line monstrosity (nice to have, but still).   The first of those
lines is all that is needed for this purpose, but the build system
still needs alternative methods for all those systems where this
doesn't work.   Something better, and more widely implemented, is needed.

Of course, the best (and therefor most costly) method is not to rely
upon some all knowing single version number, but to explicitly test
(or when necessary, ask) for all functionality that cannot simply be
assumed to exist in a known form.

kre