GCC_REQD, the NetBSD system compiler, etc

[nia <nia%NetBSD.org@localhost>]

Hi tech-pkg,

A slowly increasing number of things in pkgsrc require
GCC 8 or newer, while netbsd-9 has GCC 7. This poses a
few problems:

- The upstream GCC support is not-quite-complete for a few
  architectures, from what I can tell pkgsrc GCC still has
  problems building on ARM (64 and 32).

- In bulk builds, I see mysterious errors in packages that
  depend on packages thathave set GCC_REQD to a newer version,
  particularly when linking. My understanding is that GCC_REQD
  _must_ be set in buildlink3, but this does not completely solve
  the problem. Mixed libstdc++ versions is probably not too
  healthy. I don't really understand what's going on here.

I can see two ways out:

- pkgsrc packages should be held back from depending on compilers
  that aren't yet in a stable NetBSD release. Right now this
  would only affect a handful of unimportant leaf packages.

- NetBSD has to bootstrap a newer compiler to use pkgsrc...
  More effort into syncing patches between NetSBD and pkgsrc.