llvm dev - Jan 2014 - [LLVMdev] Sample Project can't reference llvm headers

The sample project (project/sample) builds fine out of the tree until you
try to use a llvm header.  What is the correct way to get this sample
project access to the llvm headers?

/* LLVM Header File*/
#include "llvm/Support/DataTypes.h"


llvm[2]: Compiling sample.c for Release+Asserts build
sample.c:14:10: fatal error: 'llvm/Support/DataTypes.h' file not found
#include "llvm/Support/DataTypes.h"
         ^
1 error generated.
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