Heads up: users of the netbsd-8 branch

[Martin Husemann <martin%duskware.de@localhost>]

If you are using NetBSD 8 BETA already, and are not updating from the
official "daily" builds, please note:

 - The gcc internal specs have changed (rules for libgcc when building
   shared binaries). This change requires a full build of ALL binaries
   ever created with gcc 5.4.

 - Failure to do this might lead to strange/spurious fallout like we
   saw in PRs 51266 and 52326.

Please make sure to NOT do an update build next time when updating from
source, and also rebuild ALL your pkgs.

If you are upgrading by downloading new binary sets, it is enough to rebuild
all your pkgs (or wait for new binary pkgs to become available).

Sorry for the inconvenience,

Martin