sdl12-compat: constify origenv

SDL Commits
1 
From 29c825727e0ed9eba50b15ac66f1f3a0348f587e Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Wed, 8 Dec 2021 12:15:50 +0300
Subject: [PATCH] constify origenv

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

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index 8a0e9e7..5411ee3 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -1818,7 +1818,7 @@ SDL_InitSubSystem(Uint32 sdl12flags)
 #ifdef __WINDOWS__
     /* DOSBox (and probably other things), try to force the "windib" video
        backend, but it doesn't exist in SDL2. Force to "windows" instead. */
-    char *origvidenv = NULL;
+    const char *origvidenv = NULL;
     const char *env = SDL20_getenv("SDL_VIDEODRIVER");
     if (env && (SDL20_strcmp(env, "windib") == 0)) {
         origvidenv = "windib";