1404 - undefined-behavior checks using clang

While I'm at it I also explored turning on optimization. With
optimization compile+test of the chessboard app takes 10+3s, while
without optimization it takes 3+8s. So we're still better off without
optimizations in a tight debug loop. (Since we stopped tracing the big
chessboard test.)

1 files changed, 5 insertions, 0 deletions

diff --git a/test_all_layers b/test_all_layers
index 4117dde0..e4c91640 100755
--- a/test_all_layers
+++ b/test_all_layers
@@ -5,3 +5,8 @@ do
   echo "=== $f"
   ./build_and_test_until $f || exit 0
 done
+
+echo "=== chessboard"
+rm mu.cc
+make clang
+mu test chessboard.mu  # our most intensive test so far