sdl12-compat: avoid exporting drmp3 symbols.

From 12ac5f6d07028dceba21ba687e05b3d103d4d012 Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Thu, 10 Jun 2021 23:01:04 +0300
Subject: [PATCH] avoid exporting drmp3 symbols.

Closes: https://github.com/libsdl-org/sdl12-compat/pull/101
---
 src/SDL12_compat.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/src/SDL12_compat.c b/src/SDL12_compat.c
index 12f3a0c..255d37e 100644
--- a/src/SDL12_compat.c
+++ b/src/SDL12_compat.c
@@ -5815,6 +5815,12 @@ SDL_LoadWAV_RW(SDL12_RWops *rwops12, int freerwops12,
 
 /* public domain, single-header MP3 decoder for fake CD-ROM audio support! */
 #define DR_MP3_IMPLEMENTATION
+#if defined(__GNUC__) && (__GNUC__ >= 4) && \
+  !(defined(_WIN32) || defined(__EMX__))
+#define DRMP3_API __attribute__((visibility("hidden")))
+#elif defined(__APPLE__)
+#define DRMP3_API __private_extern__
+#endif
 #define DR_MP3_NO_STDIO 1
 #define DR_MP3_NO_S16 1
 #define DR_MP3_FLOAT_OUTPUT 1