Add a release note for removing the simplify-libcalls pass.

llvm-svn: 184522
diff --git a/llvm/docs/ReleaseNotes.rst b/llvm/docs/ReleaseNotes.rst
index a12aaa2..88c1c05 100644
--- a/llvm/docs/ReleaseNotes.rst
+++ b/llvm/docs/ReleaseNotes.rst
@@ -50,6 +50,10 @@
   APFloat::isIEEENormal() was renamed to APFloat::isNormal(). This ensures that
   APFloat::isNormal() conforms to IEEE-754R-2008.
 
+* The library call simplification pass has been removed.  Its functionality
+  has been integrated into the instruction combiner and function attribute
+  marking passes.
+
 * ... next change ...
 
 .. NOTE