SDL: cmake (CheckPTHREAD): remove _GNU_SOURCE define after bug #7026 fix

From d09d0aaab69f1543886dfcf185ff24822eb1284e Mon Sep 17 00:00:00 2001
From: Ozkan Sezer <[EMAIL REDACTED]>
Date: Mon, 9 Jan 2023 01:30:50 +0300
Subject: [PATCH] cmake (CheckPTHREAD): remove _GNU_SOURCE define after bug
 #7026 fix

---
 cmake/sdlchecks.cmake | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/cmake/sdlchecks.cmake b/cmake/sdlchecks.cmake
index fe31ead9a249..f3f08499bfa2 100644
--- a/cmake/sdlchecks.cmake
+++ b/cmake/sdlchecks.cmake
@@ -966,7 +966,6 @@ macro(CheckPTHREAD)
       list(APPEND SDL_CFLAGS ${PTHREAD_CFLAGS})
 
       check_c_source_compiles("
-        #define _GNU_SOURCE 1
         #include <pthread.h>
         int main(int argc, char **argv) {
           pthread_mutexattr_t attr;
@@ -977,7 +976,6 @@ macro(CheckPTHREAD)
         set(SDL_THREAD_PTHREAD_RECURSIVE_MUTEX 1)
       else()
         check_c_source_compiles("
-            #define _GNU_SOURCE 1
             #include <pthread.h>
             int main(int argc, char **argv) {
               pthread_mutexattr_t attr;
@@ -1008,7 +1006,6 @@ macro(CheckPTHREAD)
       check_include_files("pthread_np.h" HAVE_PTHREAD_NP_H)
       if (HAVE_PTHREAD_H)
         check_c_source_compiles("
-            #define _GNU_SOURCE 1
             #include <pthread.h>
             int main(int argc, char **argv) {
               pthread_setname_np(pthread_self(), \"\");