Merge "Word the section about libc++ more strongly." into mnc-mr-docs

<h4>Compatibility</h4>

<p>Around 99% of tests pass when compiling {@code libc++} with Clang 3.4 for all supported ABIs.

The failures are mostly in the areas of {@code wchar_t} and locales that Android bionic

doesn't support. Switching locale from the default produces the following warning in

{@code logcat}:</p>

<p>The NDK's libc++ is not stable. Not all the tests pass, and the test suite is not comprehensive.

Some known issues are:</p>

<ul>

    <li>Using {@code c++_shared} on ARM can crash when an exception is thrown.</li>

    <li>Support for {@code wchar_t} and the locale APIs is limited.</li>

</ul>

<p>You should also make sure to check the "Known Issues" section of the changelog for the NDK

release you are using.</p>

<p class="note"><strong>Warning: </strong>Attempting to change to an unsupported locale will

<strong>not</strong> fail. The operation will succeed, but the locale will not change and the

following message will appear in {@code logcat}.</p>

<pre>

newlocale() WARNING: Trying to set locale to en_US.UTF-8 other than "", "C" or "POSIX"