Windows builds on AppVeyor CI

[akashche]

FYI, I've set up AppVeyor job for building graal-jvmci-8 on windows:

• appveyor.yml
• build example

It would be great to add AppVeyor integration for this repo. I am not creating a PR for the following reasons:

• RH-flavoured jdk8-win is used as a base in my setup, it may be better to use jdk8-win from AdoptOpenJDK
• minor changes were required to graal-jvmci-8 to pass the unit tests and minor changes were also required to both graal and graaljs to build them on windows and run with JVMCI

These changes are very "hacky" and need to be reworked by someone with better understanding of Graal build system.

[pejovica]

I'm working on our Windows support, and I've looked at your changes. Most of them are already being handled (e.g., I'm dealing with the Truffle NFI at the moment), so as soon as all the fixes are pushed, they shouldn't be needed anymore.

Also, once everything is done, we will provide the binaries here as releases.