pkgsrc-2017Q3 installation on 6.1.5 i386

["Nick B. (lists)" <nick.netbsd%nowindows.net@localhost>]

I had a working pkgsrc-2016Q3 on my system. I decided to upgrade this to 
pkgsrc-2017Q3.

Various packages fail to build. Can I define a later version of gcc 
(gcc48) in /usr/pkg/etc/mk.conf so it gets built and is then used to 
build everything else from pkgsrc? From reading the pkgsrc guide it 
appears that I need to add
GCC_REQD=4.8
to mk.conf to force this. If this isn't the best way to get up and 
running I'd be grateful for some guidance.

Thanks,
Nick.