build: windows sharedlib support

Added "dll" option to vcbuild.bat
Insure that Unix SO name is not used on Windows (i.e. produce a .dll file)
Insure that Node and its V8 dependency link against the Visual C++ Runtime
dynamically.
Requires backported V8 patch, see PR 7802.

Ref: https://github.com/nodejs/node/pull/7802

PR-URL: https://github.com/nodejs/node/pull/7487


Reviewed-By: Alexis Campailla <alexis@janeasystems.com>
Reviewed-By: Michael Dawson <michael_dawson@ca.ibm.com>