Fix header guard in BasicBlockTracer.h

Updated the header guard macro from LLVM_TRANSFORMS_YK_HELLOWORLD_H to
LLVM_TRANSFORMS_YK_BASIC_BLOCK_TRACER_H to accurately reflect the file name
and purpose.

llvm/include/llvm/Transforms/Yk/BasicBlockTracer.h

@@ -1,5 +1,5 @@
-#ifndef LLVM_TRANSFORMS_YK_HELLOWORLD_H
-#define LLVM_TRANSFORMS_YK_HELLOWORLD_H
+#ifndef LLVM_TRANSFORMS_YK_BASIC_BLOCK_TRACER_H
+#define LLVM_TRANSFORMS_YK_BASIC_BLOCK_TRACER_H
 
 #include "llvm/Pass.h"