progs/tests: compile with SCons and glew

Also get mingw cross-compilation of these tests working
diff --git a/progs/SConscript b/progs/SConscript
index 1670f97..71db283 100644
--- a/progs/SConscript
+++ b/progs/SConscript
@@ -3,6 +3,7 @@
     'demos/SConscript',
     'redbook/SConscript',
     'samples/SConscript',
+    'tests/SConscript',
     'trivial/SConscript',
     'vp/SConscript',
     'vpglsl/SConscript',