pkgsrc compiler on -8 (was: building lang/llvm with pkgsrc clang)

[Edgar Fuß <ef%math.uni-bonn.de@localhost>]

> The base compiler is GCC 10, built from pkgsrc-joyent.  While clang works, I
> wouldn't recommend using it, the base compiler will always provide the best
> experience and avoid conflicts with libgcc/libstdc++ etc.
But how to build on NetBSD-8, where the base GCC is too old for many packages?

1. Just build. That will lead to some packages being built with base GCC and 
   others with pkgsrc GCC. I was told that can cause problems with C++.

2. Bootstrap (different LOCALBASE etc) clang. That leads to libc++ issues.

3. Bootstrap (different LOCALBASE etc) gcc. That gives a circular dependency.

There must be a sane way to build packages on NetBSD-8, no?
I'm not talking about Firefox et. al., but of severish things like squid4 
and icinga2 (which needs boost).

Of course, I can try the old way of building gcc6, then delete all the 
build dependencies that where built on the way, add GCC_REQD+=6 to mk.conf 
and hope for the best. I was hoping there's a safer and saner way.