sdl12-compat: Apple platforms don't `#define unix`.

From b1abd1b3da5ba9ac4e943160c72b491558165712 Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Tue, 1 Jun 2021 16:13:37 -0400
Subject: [PATCH] Apple platforms don't `#define unix`.

---
 include/SDL/SDL_config.h | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/include/SDL/SDL_config.h b/include/SDL/SDL_config.h
index e9f4c2d..1a71bc0 100644
--- a/include/SDL/SDL_config.h
+++ b/include/SDL/SDL_config.h
@@ -72,7 +72,7 @@ stage, though. Send patches if your platform lacks something. */
 #define HAVE_MATH_H 1
 #endif
 
-#if defined(unix)
+#if defined(unix) || defined(__APPLE__)
 #define HAVE_ICONV_H 1
 #define HAVE_SIGNAL_H 1
 #endif
@@ -156,7 +156,7 @@ stage, though. Send patches if your platform lacks something. */
 #define HAVE_SEM_TIMEDWAIT 1
 #endif
 
-#ifdef unix
+#if defined(unix) || defined(__APPLE__)
 #define HAVE_ICONV 1
 #define HAVE_SIGACTION 1
 #define HAVE_SA_SIGACTION 1