Fix the test annotation.

Author: Vytautas Astrauskas

tests/compile-fail/concurrency/libc_pthread_create_main_terminate.rs

@@ -1,9 +1,8 @@
 // ignore-windows: Concurrency on Windows is not supported yet.
+// error-pattern: unsupported operation: the main thread terminated without waiting for other threads
 
 // Check that we terminate the program when the main thread terminates.
 
-//~^^^^ ERROR: unsupported operation: the main thread terminated without waiting for other threads
-
 #![feature(rustc_private)]
 
 extern crate libc;