Create DebugHelper.h

From now on, include DebugHelper.h for debug purpose.
diff --git a/lib/bcc/ContextManager.h b/lib/bcc/ContextManager.h
index 4267a9e..98cddfe 100644
--- a/lib/bcc/ContextManager.h
+++ b/lib/bcc/ContextManager.h
@@ -21,6 +21,7 @@
 
 #include <llvm/System/Mutex.h>
 
+#include <unistd.h>
 #include <stddef.h>