Massive PORTREVSION bump for gcc8

[Steve Kargl]

On Wed, Dec 12, 2018 at 10:29:59AM -0800, Kevin Oberman wrote:
> This morning the PORTREVISION on at least hundreds of ports was bumped
> because gcc8 was declared as the "canonical" version. As a result, I will
> have about 300 ports to rebuild which will take many hours.
> Why?
> 
> If a port is built and running properly with gcc7, I see no reason to force
> the rebuild of all of the ports that are built with gcc7. This will lead to
> a delay of probably several days in getting updated packages built for
> LATEST repos and will consume hours of CPU time for everyone using
> poudriere or building from ports. This even impacts (slightly) climate
> change with the extra energy used in rebuilding all of those ports across
> the globe.
> 
> Perhaps there was a real reason this was required. I have certainly never
> seen it before for any new compiler version to either gcc or llvm.

Does adding

DEFAULT_VERSIONS+=GCC=7

to /etc/make.conf prevent the need to update 300 ports.

-- 
Steve