Summary: Currently we depend on a single LLVM include directory. This is actually only required to define one enum, which is highly unlikely to change. THis patch makes the `Environment.h` include directory more hermetic so we no long depend on other libraries. In exchange, we get a simpler dependency list for the price of hard-coding `1` somewhere. I think it's a valid trade considering that this flag is highly unlikely to change at this point. @ronlieb AMD version https://gist.github.com/jhuber6/3313e6f957be14dc79fe85e5126d2cb3