Add note about returns_twice magic removal from LLVM itself.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@155657 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/ReleaseNotes.html b/docs/ReleaseNotes.html
index be67b6d..6af2e18 100644
--- a/docs/ReleaseNotes.html
+++ b/docs/ReleaseNotes.html
@@ -536,6 +536,9 @@
   <li>The <tt>unwind</tt> instruction is now gone. With the introduction of the
       new exception handling system in LLVM 3.0, the <tt>unwind</tt> instruction
       became obsolete.</li>
+  <li>LLVM 3.0 and earlier automatically added the returns_twice fo functions
+      like setjmp based on the name. This functionality was removed in 3.1.
+      This affects Clang users, if -ffreestanding is used.</li>
   <li>....</li>
 </ul>