[Kaleidoscope] Fix incorrect build command in Chapter 2.

[ibadawi]

Summary

rL281945 made the Chapter 2 code use llvm::make_unique. The code was previously standalone, but it now needs to point to the llvm headers in order to build.

[ibadawi]

Ping!

I ran into this while answering this stackoverflow question: https://stackoverflow.com/questions/40307876/llvm-header-not-found-after-apt-get-install/40314920#40314920.

[lhames]

Oops. *Very* belatedly: This looks good to me. Ismail - do you have commit access? If not, I can commit on your behalf.

[ibadawi]

No worries! No, I don't have commit access -- go ahead and commit it. Thanks.

docs/tutorial/LangImpl02.rst

 There is a lot of room for extension here. You can define new AST nodes,
 extend the language in many ways, etc. In the `next
 installment <LangImpl03.html>`_, we will describe how to generate LLVM
 Intermediate Representation (IR) from the AST.
 
 Full Code Listing
 =================
 
-Here is the complete code listing for this and the previous chapter.
-Note that it is fully self-contained: you don't need LLVM or any
-external libraries at all for this. (Besides the C and C++ standard
-libraries, of course.) To build this, just compile with:
+Here is the complete code listing for this and the previous chapter. Because
+this example uses the LLVM libraries, we need to link them in in order to build
+it. To do this, use the :doc:`llvm-config </CommandGuide/llvm-config>` tool to
+inform our makefile/command line about which options to use:
 
 .. code-block:: bash
 
     # Compile
-    clang++ -g -O3 toy.cpp
+    clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -o toy
     # Run
-    ./a.out
+    ./toy
 
 Here is the code:
 
 .. literalinclude:: ../../examples/Kaleidoscope/Chapter2/toy.cpp
    :language: c++
 
 `Next: Implementing Code Generation to LLVM IR <LangImpl03.html>`_
 

docs/tutorial/LangImpl03.rst

 we'll describe how to `add JIT codegen and optimizer
 support <LangImpl4.html>`_ to this so we can actually start running
 code!
 
 Full Code Listing
 =================
 
 Here is the complete code listing for our running example, enhanced with
-the LLVM code generator. Because this uses the LLVM libraries, we need
-to link them in. To do this, we use the
-`llvm-config <http://llvm.org/cmds/llvm-config.html>`_ tool to inform
-our makefile/command line about which options to use:
+the LLVM code generator. As before, to build this example, use:
 
 .. code-block:: bash
 
     # Compile
     clang++ -g -O3 toy.cpp `llvm-config --cxxflags --ldflags --system-libs --libs core` -o toy
     # Run
     ./toy
 
 Here is the code:
 
 .. literalinclude:: ../../examples/Kaleidoscope/Chapter3/toy.cpp
    :language: c++
 
 `Next: Adding JIT and Optimizer Support <LangImpl04.html>`_