build: enable small-icu support for build-release

On Windows, when building the "build-release" rule, enable both small-icu
and download-all.

This change also slightly refactors the build-release rule, mainly so that
it's easier to read.

The resulting MSI package was tested on Windows 7.

Fixes #9099.

PR: #9100
PR-URL: https://github.com/joyent/node/pull/9100


Reviewed-By: Steven R. Loomis <srloomis@us.ibm.com>
Reviewed-By: Timothy J Fontaine <tjfontaine@gmail.com>