Add Changelog entry for clang test-ref-configs.pl fix
diff --git a/ChangeLog b/ChangeLog
index be28645..f285381 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -1,5 +1,10 @@
 mbed TLS ChangeLog (Sorted per branch, date)
 
+= mbed TLS x.x.x branch released xxxx-xx-xx
+
+Bugfix
+   * Fix to allow test-ref-config.pl to build with Clang. Fixes #1628.
+
 = mbed TLS 2.16.0 branch released 2018-12-21
 
 Features