Update the getting started documentation to match the corresponding LLVM commit in r303912.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@303913 91177308-0d34-0410-b5e6-96231b3b80d8

www/get_started.html

@@ -196,6 +196,10 @@ Visual Studio:</p>
     <li><tt>mkdir build</tt> (for building without polluting the source dir)</li>
     <li><tt>cd build</tt></li>
     <li>If you are using Visual Studio 2013:  <tt>cmake -G "Visual Studio 12" ..\llvm</tt></li>
+    <li>By default, the Visual Studio project files generated by CMake use the
+     32-bit toolset. If you are developing on a 64-bit version of Windows and
+     want to use the 64-bit toolset, pass the ``-Thost=x64`` flag when
+     generating the Visual Studio solution. This requires CMake 3.8.0 or later.</li>
     <li>See the <a href="http://www.llvm.org/docs/CMake.html">LLVM CMake guide</a> for
         more information on other configuration options for CMake.</li>
     <li>The above, if successful, will have created an LLVM.sln file in the