Add needs-unwind to tests that depend on panicking

This directive isn't automatically set by compiletest or x.py, but can
be turned on manually for targets that require it.

src/test/ui/runtime/rt-explody-panic-payloads.rs

@@ -1,4 +1,5 @@
 // run-pass
+// needs-unwind
 // ignore-emscripten no processes
 // ignore-sgx no processes
 // ignore-wasm32-bare no unwinding panic