LLVM OpenMP TR4E Alpha Release

The LLVM OpenMP runtime system, extended with loop scheduling callbacks and an augmented task creation callback. The release is said to be alpha to signal that the extensions require tests and code review before it is ready to be merged into the upstream (should the extensions be accepted).

The accompanying modified version of Clang is available at:

https://github.com/LangdalP/clang/tree/pedervl/static-chunks-conditional

Disclaimer: I only created the extensions. I did not create the runtime system itself, nor did I write the excellent support for the OMPT API.