sdl2-compat: cmake: Make sure we build with -fvisibility=hidden

SDL Commits
1 
From c992bb171f945e8bacf93ce50a05ec2036e099ca Mon Sep 17 00:00:00 2001
From: "Ryan C. Gordon" <[EMAIL REDACTED]>
Date: Tue, 29 Nov 2022 14:16:29 -0500
Subject: [PATCH] cmake: Make sure we build with -fvisibility=hidden

---
 CMakeLists.txt | 4 ++++
 1 file changed, 4 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index bcc6381..0cde4a9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -125,6 +125,10 @@ target_include_directories(SDL2
 set(EXTRA_CFLAGS )
 if(CMAKE_C_COMPILER_ID MATCHES "Clang|GNU")
   set(EXTRA_CFLAGS "${EXTRA_CFLAGS} -Wall")
+  check_c_compiler_flag(-fvisibility=hidden HAVE_FVISIBILITY_HIDDEN)
+  if(HAVE_FVISIBILITY_HIDDEN)
+    set(EXTRA_CFLAGS "${EXTRA_CFLAGS} -fvisibility=hidden")
+  endif()
   check_c_compiler_flag(-Wdeclaration-after-statement HAVE_WDECLARATION_AFTER_STATEMENT)
   if(HAVE_WDECLARATION_AFTER_STATEMENT)
     set(EXTRA_CFLAGS "${EXTRA_CFLAGS} -Wdeclaration-after-statement")