doc: releases: release-notes: 3.7: mention deprecation of CSTD

Add an entry that the CSTD cmake property is deprecated and replaced
with a kconfig choice.

Signed-off-by: Pieter De Gendt <[email protected]>

Author: pdgendt

doc/releases/release-notes-3.7.rst

@@ -95,6 +95,12 @@ Build system and Infrastructure
 
 * CI-enabled blackbox tests were added in order to verify correctness of the vast majority of Twister flags.
 
+* Compiler
+
+  * Deprecated the global CSTD cmake property in favor of the :kconfig:option:`CONFIG_STD_C`
+    choice to select the C Standard version. Additionally subsystems can select a minimum
+    required C Standard version, with for example :kconfig:option:`CONFIG_REQUIRES_STD_C11`.
+
 Drivers and Sensors
 *******************