[Kaleidoscope] doc fix

[SjoerdMeijer]

Summary

Chapter 2 says that the first code example can be compiled with:

clang++ -g -O3 toy.cpp

but this doesn't compile because of the use of:

llvm::make_unique

One way to solve this is to change this to std::make_unique and add -std=c++-14
to the command line. But since the tutorial's aim is to use LLVM anyway, a
minimal change is to just add llvm-config --cxxflags.

[silvas]

LGTM with a nit.

docs/tutorial/LangImpl02.rst

719

Please use something like this verbiage that is present in LangImpl03+

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:

[SjoerdMeijer]

Thanks! And I will fix this before committing.

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:
+To build this, just compile with:
 
 .. code-block:: bash
 
     # Compile
-    clang++ -g -O3 toy.cpp
+    clang++ -g -O3 toy.cpp `llvm-config --cxxflags`
     # Run
     ./a.out
 
 Here is the code:
 
 .. literalinclude:: ../../examples/Kaleidoscope/Chapter2/toy.cpp
    :language: c++
 
 `Next: Implementing Code Generation to LLVM IR <LangImpl03.html>`_