Fix warnings from mingw64 in timing.c

Backport from dda52139 from the 1.3 branch
diff --git a/ChangeLog b/ChangeLog
index 7ee4050..69ecd60 100644
--- a/ChangeLog
+++ b/ChangeLog
@@ -7,6 +7,7 @@
      crash it remotely (found by Caj Larsson).
 
 Bugfix
+   * Fix warnings from mingw64 in timing.c (found by kxjklele).
    * Fix potential unintended sign extension in asn1_get_len() on 64-bit
      platforms (found with Coverity Scan).