Word the section about libc++ more strongly.

The libc++ support is still pretty awful. We need to make it clear that
this is something people should only be using if they are confident in
their testing.

The test details are out of date (and I don't believe they were ever
correct), and always will be since this is under active development.
Drop the specifics and just list some big KIs. Also mention that users
should check the changelog for other KIs.

Bug: http://b/21711315
Change-Id: I42f0c8ab963d7f77462b89335cf0d66cf6035388

docs/html/ndk/guides/cpp-support.jd

@@ -204,10 +204,20 @@ LOCAL_LDLIBS += -latomic
 
 <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"