progs/tests: compile with SCons and glew

Also get mingw cross-compilation of these tests working
diff --git a/progs/tests/fog.c b/progs/tests/fog.c
index ecd9f53..b6cea8c 100644
--- a/progs/tests/fog.c
+++ b/progs/tests/fog.c
@@ -30,10 +30,10 @@
  * Test to exercise fog modes and for comparison with GL_EXT_fog_coord.
  */
 
-#define GL_GLEXT_PROTOTYPES
 #include <stdio.h>
 #include <stdlib.h>
 #include <math.h>
+#include <GL/glew.h>
 #include <GL/glut.h>
 
 static int Width = 600;
@@ -190,6 +190,7 @@
    glutInitWindowSize( Width, Height );
    glutInitDisplayMode( GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH );
    glutCreateWindow(argv[0]);
+   glewInit();
    glutReshapeFunc( Reshape );
    glutKeyboardFunc( Key );
    glutDisplayFunc( Display );