Include paths prevent hermetically sealed builds

I am trying to port ChakraCore to [Buck Build](https://buckbuild.com), but the include paths used in ChakraCore are making this difficult.

For instance:

- `RuntimeBasePch.h` contains `#include "Runtime.h"`;
- `Runtime.h` contains `#include "../JITIDL/JITTypes.h"`.

This causes the compiler to walk outside of the top-level of the build, which breaks reproducibility.

This scenario is avoidable if a path without `../` is used instead. For example:

```
#include "JITIDL/JITTypes.h"
```

Or better yet, something like this:

```
#include
```

Ideally, all headers would be included from the same include-path. This is common practice is many C++ libraries, such as [Boost](https://github.com/boostorg/graph/blob/develop/include/boost/graph/subgraph.hpp#L19).

What are the ChakraCore team's thoughts on this?