compiletest: Add a `//@ needs-threads` directive

This commit is extracted from #122036 and adds a new directive to the
`compiletest` test runner, `//@ needs-threads`. This is intended to
capture the need that a target must implement threading to execute a
specific test, typically one that uses `std::thread`. This is primarily
done for WebAssembly targets which currently do not have threads by
default. This enables transitioning a lot of `//@ ignore-wasm*`-style
ignores into a more self-documenting `//@ needs-threads` directive.
Additionally the `wasm32-wasi-preview1-threads` target, for example,
does actually have threads, but isn't tested in CI at this time. This
change enables running these tests for that target, but not other wasm
targets.

1 files changed, 1 insertions, 1 deletions

diff --git a/tests/ui/threads-sendsync/sendfn-spawn-with-fn-arg.rs b/tests/ui/threads-sendsync/sendfn-spawn-with-fn-arg.rs
index 5306d69a7d2..63cf3ff4049 100644
--- a/tests/ui/threads-sendsync/sendfn-spawn-with-fn-arg.rs
+++ b/tests/ui/threads-sendsync/sendfn-spawn-with-fn-arg.rs
@@ -1,5 +1,5 @@
 //@ run-pass
-//@ ignore-emscripten no threads support
+//@ needs-threads
 
 use std::thread;