Fix OpenGL backtrace build errors, without disabling warnings.

source/blender/blenlib/BLI_system.h

@@ -28,6 +28,7 @@
 int BLI_cpu_support_sse2(void);
 
 #if defined(NDEBUG) || !defined(__BLI_UTILDEFINES_H__)
+#include <stdio.h>
 void BLI_system_backtrace(FILE *fp);
 #endif
 

source/blender/gpu/intern/gpu_debug.c

@@ -30,6 +30,7 @@
  */
 
 #include "BLI_sys_types.h"
+#include "BLI_system.h"
 
 #include "BKE_global.h"
 
@@ -43,10 +44,6 @@
 
 #define CASE_CODE_RETURN_STR(code) case code: return #code;
 
-#if (defined(__GNUC__) && !defined(__clang__)) && defined(NDEBUG)
-#  pragma GCC diagnostic ignored "-Wimplicit-function-declaration"
-#endif
-
 static const char *gpu_gl_error_symbol(GLenum err)
 {
 	switch (err) {