progs/trivial: add fflushes for cygwin
diff --git a/progs/trivial/clear-undefined.c b/progs/trivial/clear-undefined.c
index ce066bf..5ec33bf 100644
--- a/progs/trivial/clear-undefined.c
+++ b/progs/trivial/clear-undefined.c
@@ -17,6 +17,7 @@
    fprintf(stderr, "GL_VERSION    = %s\n", (char *) glGetString(GL_VERSION));
    fprintf(stderr, "GL_VENDOR     = %s\n", (char *) glGetString(GL_VENDOR));
    fprintf(stderr, "Top right corner should be red\n");
+   fflush(stderr);
 }
 
 static void Reshape(int width, int height)