Add Windows support for LLVM

[delthas]

This adds Windows (x86 and x86_64) support for LLVM

This PR essentially updates #407 for LLVM 5.0.1. (It also fixes #305.)

[delthas]

@saudet I think this works now. (The latest commit Travis CI build fails but it's not related to LLVM.)

[saudet]

Thanks for the contribution! Let me know if the binaries in the snapshots don't look OK for some reason:
http://bytedeco.org/builds/

[mennodenhollander]

I tested the 5.0.1-1.4.1-SNAPSHOT version. The windows dependencies are missing from the llvm-platform-5.0.1-1.4.1-SNAPSHOT.pom. To get it to work I had to explicitly add the windows dependency to my project:

<dependency>
    <groupId>org.bytedeco.javacpp-presets</groupId>
    <artifactId>llvm</artifactId>
    <version>5.0.1-1.4.1-SNAPSHOT</version>
    <classifier>windows-x86_64</classifier>
</dependency>

[saudet]

Yes, indeed, please send a pull request!