Add NaCl SDK release note about LLVM 3.6 and debug metadata changes.

native_client_sdk/doc_generated/sdk/release-notes.html

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 <section id="release-notes">
 <span id="sdk-release-notes"></span><h1 id="release-notes"><span id="sdk-release-notes"></span>Release Notes</h1>
 <p>The dates in the following release notes denote when Chrome and the NaCl SDK
 reached canary status. The stable release is typically 6 weeks later.</p>
 <h2 id="chrome-pepper-43-03-april-2015">Chrome/Pepper 43 (03 April 2015)</h2>
 <h3 id="pnacl">PNaCl</h3>
 <ul class="small-gap">
 <li>The C11/C++11 <code>acquire</code>, <code>release</code>, and <code>acq_rel</code> memory orders are now
 generated by default. The in-browser Chrome 42 translator supports them, the
 SDK can therefore generate them.</li>
 <li>Fix a <a class="reference external" href="https://code.google.com/p/chromium/issues/detail?id=460432">code generation bug on ARM</a> when dealing with 16-bit load/store and
 <code>bswap</code> which led to a NaCl validation failure.</li>
+<li>PNaCl is now based on LLVM 3.6. If you are using GDB to debug PNaCl
+<a class="reference internal" href="/native-client/devguide/devcycle/debugging.html#debugging-pnacl-pexes"><em>BC files with debug metadata in the browser</em></a>,
+remember that debug info from SDK version <code>X</code> is only compatible with the
+PNaCl translator in chrome version <code>X</code>. The bitcode debug metadata format
+changed from LLVM 3.5 to 3.6. If you need to debug an app built with SDK
+version <code>X</code> running in Chrome version <code>Y</code> (with <code>X != Y</code>), it is still
+possible to do so. Simply translate the pexe to a nexe using the
+<a class="reference internal" href="/native-client/devguide/devcycle/debugging.html#debugging-pexes-via-nexes"><em>offline pnacl-translate tool from SDK version X</em></a> instead of using the translator in the
+browser (version <code>Y</code>).</li>
 </ul>
 <h2 id="chrome-pepper-42-20-february-2015">Chrome/Pepper 42 (20 February 2015)</h2>
 <h3 id="sdk">SDK</h3>
 <ul class="small-gap">
 <li>The SDK now contains experimental versions of <code>i686-nacl-clang</code>,
 <code>x86_64-nacl-clang</code>, and <code>arm-nacl-clang</code> as well as the <code>clang++</code>
 equivalents. These toolchains are based on the same LLVM version as PNaCl, but
 can be used to generate NaCl <code>.nexe</code> files instead of translating a
 <code>.pexe</code> locally or using the GCC toolchain.</li>
 </ul>
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 </ul>
 <h3 id="id29">PPAPI</h3>
 <ul class="small-gap">
 <li>The <code>CompletionCallbackFactory</code> class template now takes a thread traits
 class as its second parameter. For details see the <a class="reference external" href="/native-client/pepper_stable/cpp/classpp_1_1_completion_callback_factory#details">CompletionCallbackFactory
 class template reference</a>.</li>
 </ul>
 </section>
 
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