Sdl12-compat: guard WIN32_LEAN_AND_MEAN definition

SDL Commits
1 
From 59df66479220a9645171d956765e7410d45ee9e9 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Fri, 19 Feb 2021 05:39:11 +0300
Subject: [PATCH] guard WIN32_LEAN_AND_MEAN definition

---
 src/SDL12_compat.c | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index b668983..17b3d42 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -762,7 +762,9 @@ static EventQueueType *EventQueueAvailable = NULL;
 
 /* Obviously we can't use SDL_LoadObject() to load SDL2.  :)  */
 #if defined(_WINDOWS)
+    #ifndef WIN32_LEAN_AND_MEAN
     #define WIN32_LEAN_AND_MEAN 1
+    #endif
     #include <windows.h>
     #define SDL20_LIBNAME "SDL2.dll"
     static HANDLE Loaded_SDL20 = NULL;