Makes LLVM optional

In order to build llst with llvm support, pass -DLLVM=ON to cmake

Issue: #9
Autodetects 64 bit architecture and sets -m32

The parameter is set only on 64-bit OS.

Now you can compile llst under Raspberry Pi or Ubuntu/i686
or Ubuntu/x86_64 without any changes in CMakelists.txt.

Issue: #9