cmd/go: fix handling of build tags for standard commands Otherwise if I add '+build !race' to e.g. src/cmd/fix/reflect_test.go, it does not work.
cmd/go: fix handling of build tags for standard commands
Otherwise if I add '+build !race' to e.g. src/cmd/fix/reflect_test.go,
it does not work.

R=golang-dev, rsc
CC=golang-dev
http://codereview.appspot.com/6642044

h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang,h8liu/golang