Added CMake support

 1. Cross platform build support
 2. Automatically detects the Clang and LLVM (based on the llvm config exe option supplied)

The LLVM_CONFIG_EXE path should point to the "llvm-config.exe" from the llvm build directory. All other related files of clang and llvm will tbe automatically populated by Cmake.

Steps to use CMake:
1. Install cmake-gui (if not already present)
2. Launch cmake-gui and press configure.
3. Set the path for the 'LLVM_CONFIG_EXE' and press 'configure' again followed by 'generate'. 

Alternately,.
1. create a build directory (mkdir build)
2. goto the build directory (cd build)
3. issue the command: cmake ..