Fixed compiler warnings in test programs by adding includes directives.

test/testlock.c

@@ -16,6 +16,7 @@
 
 #include <signal.h>
 #include <stdio.h>
+#include <stdlib.h> /* for atexit() */
 
 #include "SDL.h"
 #include "SDL_mutex.h"

test/testnative.c

@@ -12,6 +12,8 @@
 /* Simple program:  Create a native window and attach an SDL renderer */
 
 #include <stdio.h>
+#include <stdlib.h> /* for srand() */
+#include <time.h> /* for time() */
 
 #include "testnative.h"
 

test/testshader.c

@@ -11,6 +11,7 @@
 */
 /* This is a simple example of using GLSL shaders with SDL */
 
+#include <stdio.h> /* for printf() */
 #include "SDL.h"
 
 #ifdef HAVE_OPENGL