misc/makerelease: use windows installer resources from local goroot
misc/makerelease: use windows installer resources from local goroot

This broke when we renamed the tool, and I missed this fix when I
fixed darwin last week.

LGTM=minux.ma, bradfitz
R=golang-codereviews, minux.ma, bradfitz
CC=golang-codereviews
https://codereview.appspot.com/70670043

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