Mention the changes in the handling of language linkage in the release notes.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@179094 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/docs/ReleaseNotes.rst b/docs/ReleaseNotes.rst
index d9a3364..fbcd1ef 100644
--- a/docs/ReleaseNotes.rst
+++ b/docs/ReleaseNotes.rst
@@ -81,6 +81,12 @@
 C++ Language Changes in Clang
 -----------------------------
 
+- Clang now correctly implements language linkage for functions and variables.
+  This means that, for example, it is now possible to overload static functions
+  declared in an ``extern "C"`` context. For backwards compatibility, an alias
+  with the unmangled name is still emitted if it is the only one and has the
+  ``used`` attribute.
+
 C++11 Feature Support
 ^^^^^^^^^^^^^^^^^^^^^