Add support for a Windows Build

[alexw91]

Looks like Travis doesn't support a Windows build yet: travis-ci/travis-ci#2104
Neither does AWS CodeBuild, but according to this blog post from December :

We are launching with support for Linux builds and are planning to add support for Windows in the near future.

It looks like AWS CodeBuild may be adding Windows support soon.

EDIT: Looks like Appveyor currently supports a Windows build: https://www.appveyor.com/

Code that would have to be fixed or replaced for a Windows build:

• Replace dev/urandom with Windows equivalent
• TCP Corking IO API's?
• MVSC compatible alternative to __attribute__((cleanup))

[JonathanHenson]

/dev/urandom replacement example is here:

https://github.com/aws/aws-sdk-cpp/blob/master/aws-cpp-sdk-core/source/utils/crypto/bcrypt/CryptoImpl.cpp#L42

[JonathanHenson]

I'll add, it may make sense to not link to libcrypto on windows and use CNG instead.

[YashC]

@alexw91 @JonathanHenson Any timeline for Windows support?

[zaherd]

@YashC Thanks for reaching out regarding this issue . Currently, Windows support is not on our immediate roadmap. We will take your request into consideration in a future release. We will update this issue once we have a potential date.