win,build: forward release_urlbase to configure

The RELEASE_URLBASE environment variable is used in releases as
a prefix for links in the process.release object. The Makefile picks
it and forwards it to configure, but vcbuild.bat did not. Hence, in
Windows, Node releases have a correct process.release because it uses
the default URL, but nightlies, RCs and so on do not, breaking
node-gyp. This enables native modules to be built with such versions
of Node.

PR-URL: https://github.com/nodejs/node/pull/8430


Reviewed-By: jbergstroem - Johan Bergström <bugs@bergstroem.nu>