tests: build two-panic-runtimes.rs with -Cpanic=unwind

Author: jieyouxu

tests/ui/panic-runtime/two-panic-runtimes.rs

@@ -1,10 +1,10 @@
 // ignore-tidy-linelength
 //@ build-fail
-//@ dont-require-annotations: ERROR
 //@ dont-check-compiler-stderr
 //@ aux-build:panic-runtime-unwind.rs
 //@ aux-build:panic-runtime-unwind2.rs
 //@ aux-build:panic-runtime-lang-items.rs
+//@ compile-flags: -Cpanic=unwind
 
 #![no_std]
 #![no_main]
@@ -16,7 +16,3 @@ extern crate panic_runtime_lang_items;
 fn main() {}
 
 //~? ERROR cannot link together two panic runtimes: panic_runtime_unwind and panic_runtime_unwind2
-// FIXME: These errors are target-dependent, could be served by some "optional error" annotation
-// instead of `dont-require-annotations`.
-//FIXME~? ERROR the linked panic runtime `panic_runtime_unwind2` is not compiled with this crate's panic strategy `abort`
-//FIXME~? ERROR the crate `panic_runtime_unwind` requires panic strategy `unwind` which is incompatible with this crate's strategy of `abort`