Add windows C++ targets

[GeorgeLS]

I tweaked the CMakefiles so that you can compile for both x86/x64 and generate different output structure.
This makes the output way cleaner and also doesn't confuse mayhem package by picking other PDBs from previously compiled artifacts.

I also updated the README file with instructions for compiling x86/x64 targets on Windows.

[xansec]

I have an idea for this:

1. Create a Linux and Windows folder under each language where Windows is supported (currently only C++ and C#)
2. The Windows folder will include, for example, libfuzzer or base, and each supported compiler.
   3 Remove the Cmake and invoke directly in Docker (I suggest maybe doing multi-stage where the first stage is in windows, like https://hub.docker.com/r/microsoft/windows, and the second stage is just vanilla ubuntu, and we copy the executables from the build stage).

Would that work better? Here's an example of what I'm thinking:
https://github.com/ForAllSecure/mayhem-examples/tree/windows-targets-suggested-dir-structure

[xansec]

I think this can be closed as is superseded by #50

[xansec]

I was wrong - #50 was merged into this. We should now merge this.