jit factory - use clang api

[guruofquality]

Currently we execute the clang binary to get llvm bitcode. It should be possible to use the clang api to directly compile code and get an llvm Module. Some work here: https://github.com/guruofquality/grextras/tree/use_clang_api

However, ubuntu 12.10 has a clangdev missing important libraries. 13.04 has the working dev package. So users dont have to manually install clang-dev from source... we dont want to force the api usage option.

So when I get around to upgrading my ubuntu -- do an ifdef to support both executing and API.

[guruofquality]

What a hole. The clang api doesnt include any of the c++ default headers paths:

• http://lists.cs.uiuc.edu/pipermail/cfe-dev/2012-October/025134.html