Add instructions for building LLDB on Mac OS X with CMake

[xiaobai]

Summary

There were previously no instructions for building LLDB on Mac OS X
with CMake. It's sufficiently close to building on Linux/FreeBSD/NetBSD that a
well-motivated developer could figure out the steps themselves. However, having
an explicit guide is better and can provide Mac OS X specific configurations
(e.g. LLDB_BUILD_FRAMEWORK).

[xiaobai]

Reducing redundancy and changing some wording around.

[labath]

Makes sense to me.

www/build.html

<div id="content">
               in Visual Studio, set <code>lldb</code> as the startup project, and use F5 to run it.  You need only edit the project
               settings to set the executable and the working directory to point to binaries inside of the <code>ninja</code> tree.
             </p>
           </div>
         </div>
         <div class="post" id="BuildingLldbOnMacOSX">
           <h1 class="postheader">Building LLDB on Mac OS X</h1>
           <div class="postcontent">
-            <p>Building on Mac OS X is as easy as downloading the code and building the Xcode project or workspace:</p>
+            <p> There are two ways to build LLDB on Mac OS X: Using Xcode and using CMake
           </div>
           <div class="postcontent">
             <h2>Preliminaries</h2>
             <ul>
               <li>XCode 4.3 or newer requires the "Command Line Tools" component (XCode->Preferences->Downloads->Components).</li>
               <li>Mac OS X Lion or newer requires installing <a href="http://swig.org">Swig</a>.</li>
             </ul>
-            <h2>Building LLDB</h2>
+            <h2>Building LLDB with Xcode</h2>
+            <p>Building on Mac OS X with Xcode is as easy as downloading the code and building the Xcode project or workspace:</p>
             <ul>
               <li><a href="download.html">Download</a> the lldb sources.</li>
               <li>Follow the code signing instructions in <b>lldb/docs/code-signing.txt</b></li>
               <li>In Xcode 3.x: <b>lldb/lldb.xcodeproj</b>, select the <b>lldb-tool</b> target, and build.</li>
               <li>In Xcode 4.x: <b>lldb/lldb.xcworkspace</b>, select the <b>lldb-tool</b> scheme, and build.</li>
             </ul>
+            <h2>Building LLDB with CMake</h2>
+            <p> First download the LLVM, Clang, and LLDB sources. Refer to <a href="source.html">this page</a> for precise instructions on this step.</p>
+            <p> Refer to the code signing instructions in <b>lldb/docs/code-signing.txt</b> for info on codesigning debugserver during the build.</p>
+            <p> Using CMake is documented on the <a href="http://llvm.org/docs/CMake.html">Building LLVM with CMake</a> page.
+            Ninja is the recommended generator to use when building LLDB with CMake.</p>
+            <code>
+              &gt; cmake $PATH_TO_LLVM -G Ninja
+              <br />&gt; ninja lldb
+            </code>
+            <p>
+               As noted in the "Building LLVM with CMake" page mentioned above, you can pass
+               variables to cmake to change build behavior. If LLDB is built as a part of LLVM,
+               then you can pass LLVM-specific CMake variables to cmake when building LLDB.
+            </p>
+            <p>Here are some commonly used LLDB-specific CMake variables:</p>
+            <ul>
+              <li><code><b>LLDB_EXPORT_ALL_SYMBOLS</b>:BOOL </code>: Exports all symbols. Useful in conjunction with CMAKE_BUILD_TYPE=Debug.</li>
+              <li><code><b>LLDB_BUILD_FRAMEWORK</b>:BOOL </code>: Builds LLDB.framework as Xcode would</li>
+              <li><code><b>LLDB_CODESIGN_IDENTITY</b>:STRING </code>: Determines the codesign identity to use. An empty string means skip building debugserver to avoid codesigning.</li>
+            </ul>
           </div>
           <div class="postfooter"></div>
         </div>
         <div class="post" id="BuildingLldbOnLinux">
           <h1 class="postheader">Building LLDB on Linux, FreeBSD and NetBSD</h1>
           <div class="postcontent">
             <p>This document describes the steps needed to compile LLDB on most Linux systems, FreeBSD and NetBSD.</a></p>
           </div>