progs/trivial: Use glew where needed.

Builds on windows now.
diff --git a/progs/trivial/tri-fp-const-imm.c b/progs/trivial/tri-fp-const-imm.c
index 7111380..9e2c63a 100644
--- a/progs/trivial/tri-fp-const-imm.c
+++ b/progs/trivial/tri-fp-const-imm.c
@@ -25,7 +25,7 @@
 #include <stdio.h>
 #include <string.h>
 #include <stdlib.h>
-#define GL_GLEXT_PROTOTYPES
+#include <GL/glew.h>
 #include <GL/glut.h>
 
 
@@ -159,6 +159,8 @@
 	exit(1);
     }
 
+    glewInit();
+
     Init();
 
     glutReshapeFunc(Reshape);