build: update comment about GO_LDFLAGS. (5l/6l/8l aren't involved in building packages)
build: update comment about GO_LDFLAGS.
(5l/6l/8l aren't involved in building packages)

R=golang-dev, robert.hencke
CC=golang-dev
http://codereview.appspot.com/5798071

gnanderson/go,pombredanne/go-deleteme,dsriram/golang,tv42/old-go,apparentlymart/golang,dsriram/golang,gnanderson/go,gnanderson/go,apparentlymart/golang,tv42/old-go,apparentlymart/golang,dsriram/golang,dsriram/golang,tv42/old-go,tv42/old-go,gnanderson/go,tv42/old-go,tv42/old-go,dsriram/golang,dsriram/golang,pombredanne/go-deleteme,apparentlymart/golang,pombredanne/go-deleteme,pombredanne/go-deleteme,pombredanne/go-deleteme,dsriram/golang,apparentlymart/golang,apparentlymart/golang,pombredanne/go-deleteme,tv42/old-go,gnanderson/go,apparentlymart/golang,gnanderson/go,pombredanne/go-deleteme,gnanderson/go