add a note about c99
diff --git a/Doc/whatsnew/3.6.rst b/Doc/whatsnew/3.6.rst
index 66f6b85..f2b53fb 100644
--- a/Doc/whatsnew/3.6.rst
+++ b/Doc/whatsnew/3.6.rst
@@ -845,6 +845,9 @@
Build and C API Changes
=======================
+* Python now requires some C99 support in the toolchain to build. For more
+ information, see :pep:`7`.
+
* The ``--with-optimizations`` configure flag has been added. Turning it on
will activate LTO and PGO build support (when available).
(Original patch by Alecsandru Patrascu of Intel in :issue:`26539`.)