Detect crashes in frog/leg (when running on VM).

dart/frog/frogc.dart

Index: dart/frog/frogc.dart
diff --git a/dart/frog/frogc.dart b/dart/frog/frogc.dart
index df6aca1f6c29c2a3887d920ea871ee4d1d9b97b9..f1f7a2fbc9a7d09ec30d425fafb37496e6f7db18 100644
--- a/dart/frog/frogc.dart
+++ b/dart/frog/frogc.dart
@@ -8,5 +8,18 @@
 
 void main() {
   lang.legCompile = leg.compile;
-  minfrogc.main();
+  try {
+    minfrogc.main();
+  } catch (var exception, var trace) {
+    try {
+      print('Internal error: $exception');
+    } catch (var ignored) {
+      print('Internal error: error while printing exception');
+    }
+    try {
+      print(trace);
+    } finally {
+      exit(253);
+    }
+  }
 }