Rollup merge of #125988 - GuillaumeGomez:migrate-run-make-used, r=jieyouxu

Migrate `run-make/used` to `rmake.rs`

Part of #121876.

r? `@jieyouxu`

Author: GuillaumeGomez

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -228,7 +228,6 @@ run-make/unknown-mod-stdin/Makefile
 run-make/unstable-flag-required/Makefile
 run-make/use-suggestions-rust-2018/Makefile
 run-make/used-cdylib-macos/Makefile
-run-make/used/Makefile
 run-make/volatile-intrinsics/Makefile
 run-make/wasm-exceptions-nostd/Makefile
 run-make/wasm-override-linker/Makefile

tests/run-make/used/Makefile

@@ -0,0 +1,15 @@
+// This test ensures that the compiler is keeping static variables, even if not referenced
+// by another part of the program, in the output object file.
+//
+// It comes from #39987 which implements this RFC for the #[used] attribute:
+// https://rust-lang.github.io/rfcs/2386-used.html
+
+//@ ignore-msvc
+
+use run_make_support::{cmd, rustc};
+
+fn main() {
+    rustc().opt_level("3").emit("obj").input("used.rs").run();
+
+    cmd("nm").arg("used.o").run().assert_stdout_contains("FOO");
+}