SDL_rtf: Use CMAKE_CURRENT_*_DIR instead of CMAKE_*_DIR

SDL Commits
1 
From ea0adee7abd80b9830d2b89183b5e36db47c4c3a Mon Sep 17 00:00:00 2001
From: Anonymous Maarten <[EMAIL REDACTED]>
Date: Thu, 5 Oct 2023 19:09:40 +0200
Subject: [PATCH] Use CMAKE_CURRENT_*_DIR instead of CMAKE_*_DIR

---
 CMakeLists.txt | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 29c2381..5f5b497 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -10,7 +10,7 @@ set(SDL_REQUIRED_VERSION 3.0.0)
 
 set(SDLTTF_REQUIRED_VERSION 3.0.0)
 
-if(CMAKE_SOURCE_DIR STREQUAL CMAKE_BINARY_DIR)
+if(CMAKE_CURRENT_SOURCE_DIR STREQUAL CMAKE_CURRENT_BINARY_DIR)
     message(FATAL_ERROR "Prevented in-tree built. Please create a build directory outside of the SDL_rtf source code and call cmake from there")
 endif()