/cc @orangemocha @indutny

P.S. this is the output on compiling the node target with all warnings enabled:
https://gist.github.com/refack/65eb7b126e1c9b697134

Refactored the whole thing.

Some nits, but mostly LGTM

Dropped the whole style fix commit.
I still need convincing about 'WarnAsError'. Again it's MSVS only, and it works. The compiler is our friend why not use it. If someone introduces a new warning to the windows build someone must look at it.
The logic behind 'cflags!': ['-Werror'] is explained in the comment, but here it's a specific compiler suite on a specific OS why let it accumulate warnings, as it has till now.

rebased on #8476

Most developers build/test their changes on one platform. Since not everybody builds on Windows, treating warning as errors will cause a lot of build breaks!
I hope that one day we will have a better continuous integration infrastructure that will build/test every PR on all platforms. If we had that, we could turn WarnAsError on, but until then I believe it will bring more trouble than benefit.