SDL: cmake: do all compile tests with -D_GNU_SOURCE=1 (460b7)

SDL Commits
1 
From 460b7b247f0046bda8b49242435924d03ea9f608 Mon Sep 17 00:00:00 2001
From: Anonymous Maarten <[EMAIL REDACTED]>
Date: Sun, 8 Jan 2023 19:12:11 +0100
Subject: [PATCH] cmake: do all compile tests with -D_GNU_SOURCE=1

---
 CMakeLists.txt | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/CMakeLists.txt b/CMakeLists.txt
index e539ffb6d0a9..5c494c5e5d72 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -289,6 +289,8 @@ if(WINDOWS)
   set(CMAKE_SHARED_LIBRARY_PREFIX "")
 endif()
 
+set(CMAKE_REQUIRED_FLAGS "${CMAKE_REQUIRED_FLAGS} -D_GNU_SOURCE=1")
+
 # Emscripten toolchain has a nonempty default value for this, and the checks
 # in this file need to change that, so remember the original value, and
 # restore back to that afterwards. For check_function_exists() to work in