progs/tests: compile with SCons and glew

Also get mingw cross-compilation of these tests working
diff --git a/progs/tests/floattex.c b/progs/tests/floattex.c
index dd6d882..dd99d83 100644
--- a/progs/tests/floattex.c
+++ b/progs/tests/floattex.c
@@ -8,6 +8,7 @@
 #include <stdio.h>
 #include <stdlib.h>
 #include <math.h>
+#include <GL/glew.h>
 #include <GL/glut.h>
 #include "extfuncs.h"
 #include "readtex.h"
@@ -230,6 +231,7 @@
    glutInitWindowSize(400, 400);
    glutInitDisplayMode(GLUT_RGB | GLUT_DOUBLE | GLUT_DEPTH);
    glutCreateWindow(argv[0]);
+   glewInit();
    glutReshapeFunc(Reshape);
    glutKeyboardFunc(Key);
    glutDisplayFunc(Draw);