6l: change default output name to 6.out.exe on windows
6l: change default output name to 6.out.exe on windows

R=golang-dev, vcc.163
CC=golang-dev
http://codereview.appspot.com/4670049
abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go,abustany/go