thread name setting works with strict provenance now :)

Author: RalfJung

tests/run-pass/concurrency/simple.rs

@@ -1,5 +1,5 @@
 // ignore-windows: Concurrency on Windows is not supported yet.
-// compile-flags: -Zmiri-check-number-validity
+// compile-flags: -Zmiri-strict-provenance
 
 use std::thread;