cmake: removed an add_definitions call.
diff --git a/cmake/sdlchecks.cmake b/cmake/sdlchecks.cmake
index ea2a421..3977745 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()