SDL: Update 2.0.18 release notes with CMake prefix change

From b7a0200aab8088e04800d33cc88fee384df0d78c Mon Sep 17 00:00:00 2001
From: Cameron Gutman <[EMAIL REDACTED]>
Date: Fri, 3 Dec 2021 17:02:30 +0300
Subject: [PATCH] Update 2.0.18 release notes with CMake prefix change

 WhatsNew.txt | 1 +
 1 file changed, 1 insertion(+)

diff --git a/WhatsNew.txt b/WhatsNew.txt
index 88ab5a3dbb..db477d358e 100644
--- a/WhatsNew.txt
+++ b/WhatsNew.txt
@@ -8,6 +8,7 @@ This is a list of major changes in SDL's version history.
 * The SDL wiki documentation and development headers are automatically kept in sync
 * Each function has information about in which version of SDL it was introduced
+* SDL-specific CMake options are now prefixed with 'SDL_'. Be sure to update your CMake build scripts accordingly!
 * Added the hint SDL_HINT_APP_NAME to let SDL know the name of your application for various places it might show up in system information
 * Added SDL_RenderGeometry() and SDL_RenderGeometryRaw() to allow rendering of arbitrary shapes using the SDL 2D render API
 * Added SDL_SetTextureUserData() and SDL_GetTextureUserData() to associate application data with an SDL texture