using gcc6 to try compiling arctic fox

Hi there,

I have NetBSD current installed on my mac mini g4, system gcc is 7 point
something as you know.  I was going to try compiling the arctic fox browser
from their git repository, which apparently builds on Linux ppc32 but only
with GCC versions below 7, albeit v slowly.
I can get GCC 6 as a package still from one of the older releases, or
perhaps if that's wrong, build it myself with pkgsrc.
I've installed the older GCC 6 package via ftp with the pkg_add command,
and it goes into the /usr/pkg/ directory under it's own directory.  As per
this guide here:  https://wiki.netbsd.org/pkgsrc/gcc/

Being inexperienced with NetBSD, if I want to experiment with building
software outside the pkgsrc system, such as with this arctic fox attempt,
how do I make sure the build will use the version of GCC I want?  i.e. I
can set the gcc version in a ".mozconfig" file, but will the build know
where to find it in NetBSD?

I'm sure this is pretty obvious to people with more experience than me.

Kevin.