* use new Make.$GOARCH files in gobuild.
 * rename 6ar to arch-generic gopack.
 * place objects in $GOROOT/pkg/$GOOS_$GOARCH
   (makes cross-compiling easier, and no one
   ever types these paths by hand anyway).

R=r
DELTA=29  (6 added, 8 deleted, 15 changed)
OCL=29923
CL=29967