Add notes about two known X86-64 limitations.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@52108 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/ReleaseNotes.html b/docs/ReleaseNotes.html
index da797b5..f34b3ca 100644
--- a/docs/ReleaseNotes.html
+++ b/docs/ReleaseNotes.html
@@ -606,6 +606,11 @@
     currently due
     to <a href="http://llvm.org/PR2255">several</a>
     <a href="http://llvm.org/PR2257">bugs</a> in FP stackifier
+  <li>The X86-64 backend does not yet support position-independent code (PIC)
+      generation on Linux targets.</li>
+  <li>The X86-64 backend does not yet support the LLVM IR instruction
+      <tt>va_arg</tt>. Currently, the llvm-gcc front-end supports variadic
+      argument constructs on X86-64 by lowering them manually.</li>
 </ul>
 
 </div>