by definition, they know what they are building for.
makes it easier to switch architectures when testing.

% 6g x.go
% 6l x.6
% 6.out
"Wed Jan 13 10:57:46 EST 2010"
% 8g x.go
% 8l x.8
% 8.out
"Wed Jan 13 10:57:46 EST 2010"
% echo $GOARCH

%

R=rsc
CC=golang-dev
https://golang.org/cl/186116