src: refactor vcbuild configure args creation
src: refactor vcbuild configure args creation

remove a bunch of variables and rely on %configure_flags% where
possible, also allow for an external %config_flags% variable to supply
additional arguments to configure to match the behaviour of the Makefile

PR-URL: https://github.com/nodejs/node/pull/3399
Reviewed-By: Johan Bergström <3e38e5ce4283f06de4b83ad13af081abc5e16740@bergstroem.nu>
Reviewed-By: James M Snell <2d64a127ffc94dbe6295928a16bedf8b26814159@gmail.com>
Reviewed-By: João Reis <5095b819f0ac7660978fa44706cfa411a9116ec5@janeasystems.com>

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