Maybe fix thread-spawn stderr?

Author: landaire

tests/run-pass/concurrency/thread-spawn.rs

@@ -1,6 +1,9 @@
 // compile-flags: -Zmiri-panic-on-unsupported -Zmiri-ignore-leaks
 // ignore-linux: Only Windows is not supported.
 // ignore-macos: Only Windows is not supported.
+// normalize-stderr-test ".*/(rust[^/]*|checkout)/library/" -> "RUSTLIB/"
+// normalize-stderr-test "RUSTLIB/(.*):\d+:\d+ "-> "RUSTLIB/$1:LL:COL "
+// normalize-stderr-test "::<.*>" -> ""
 
 use std::thread;