SDL: cmake: removed an add_definitions call.

SDL Commits
1 
From f1793af4046d294152ec15944f0e35fa8c9b9411 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Tue, 5 Oct 2021 11:19:30 -0400
Subject: [PATCH] cmake: removed an add_definitions call.

---
 cmake/sdlchecks.cmake | 1 -
 1 file changed, 1 deletion(-)

diff --git a/cmake/sdlchecks.cmake b/cmake/sdlchecks.cmake
index ea2a421e6d..39777452c3 100644
--- a/cmake/sdlchecks.cmake
+++ b/cmake/sdlchecks.cmake
@@ -442,7 +442,6 @@ macro(CheckX11)
           list(APPEND EXTRA_LIBS ipc)
         endif()
         if(NOT HAVE_SHMAT)
-          add_definitions(-DNO_SHARED_MEMORY)
           list(APPEND EXTRA_CFLAGS "-DNO_SHARED_MEMORY")
         endif()
       endif()