Fix two run-fail tests for asmjs

Use eprintln!() to make sure stdio is flushed.

src/test/run-fail/mir_drop_panics.rs

@@ -17,7 +17,7 @@ fn drop(&mut self) {
         if self.0 == 1 {
             panic!("panic 1");
         } else {
-            eprint!("drop {}", self.0);
+            eprintln!("drop {}", self.0);
         }
     }
 }

src/test/run-fail/panic-set-handler.rs

@@ -14,7 +14,7 @@
 
 fn main() {
     panic::set_hook(Box::new(|i| {
-        eprint!("greetings from the panic handler");
+        eprintln!("greetings from the panic handler");
     }));
     panic!("foobar");
 }