Enable the LLVM JIT event listener

This PR enables the LLVM JIT event listener. It was tested on Windows with LLVM 3.3 and the JIT engine. It requires that LLVM is built with INTEL_JIT_EVENTS and should have no effect otherwise.

In Vtune, each function is identified separately and it is possible to browse the assembly along with the counters.
![vtune](https://cloud.githubusercontent.com/assets/8500539/4359670/db59adfe-4273-11e4-8d17-70a1606373f2.png)

Something similar should be possible with oprofile. 

Philippe