test/run-pass/out-of-stack: prevent tco

We really do *not* want TCO to kick in. If it does, we'll never blow the
stack, and never trigger the condition the test is checking for. To that end,
do a meaningless alloc that serves only to get a destructor to run. The
addition of nocapture/noalias seems to have let LLVM do more TCO, which
hurt this testcase.

src/test/run-pass/out-of-stack.rs

@@ -28,6 +28,7 @@ fn silent_recurse() {
 fn loud_recurse() {
     println!("hello!");
     loud_recurse();
+    black_box(()); // don't optimize this into a tail call. please.
 }
 
 fn main() {