sdl2-compat: Expose SDL3 version string in SDL3_VERSION hint

SDL Commits
1 
From 91d36b8d9d06958e2663623d100d12b596675120 Mon Sep 17 00:00:00 2001
From: Cameron Gutman <[EMAIL REDACTED]>
Date: Sat, 4 Apr 2026 13:04:54 -0500
Subject: [PATCH] Expose SDL3 version string in SDL3_VERSION hint

---
 src/sdl2_compat.c | 1 +
 1 file changed, 1 insertion(+)

diff --git a/src/sdl2_compat.c b/src/sdl2_compat.c
index 6f81ebbd..3ba01349 100644
--- a/src/sdl2_compat.c
+++ b/src/sdl2_compat.c
@@ -1086,6 +1086,7 @@ LoadSDL3(void)
                         SDL2Compat_LogAtStartup(debugmsg);
                     }
                     SDL2Compat_ApplyQuirks(force_x11);  /* Apply and maybe print a list of any enabled quirks. */
+                    SDL2Compat_SetEnvAtStartup("SDL3_VERSION", sdl3verstr);
                 }
             }
             #define SDL3_SYM(rc,fn,params,args,ret) SDL3_##fn = (SDL3_##fn##_t) LoadSDL3Symbol("SDL_" #fn, &okay);