rewrite `link-dedup` to rmake

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -111,7 +111,6 @@ run-make/libtest-padding/Makefile
 run-make/libtest-thread-limit/Makefile
 run-make/link-args-order/Makefile
 run-make/link-cfg/Makefile
-run-make/link-dedup/Makefile
 run-make/link-framework/Makefile
 run-make/link-path-order/Makefile
 run-make/linkage-attr-on-static/Makefile

tests/run-make/link-dedup/rmake.rs

@@ -0,0 +1,32 @@
+// When native libraries are passed to the linker, there used to be an annoyance
+// where multiple instances of the same library in a row would cause duplication in
+// outputs. This has been fixed, and this test checks that it stays fixed.
+// With the --cfg flag, -ltestb gets added to the output, breaking up the chain of -ltesta.
+// Without the --cfg flag, there should be a single -ltesta, no more, no less.
+// See https://github.com/rust-lang/rust/pull/84794
+
+//@ ignore-msvc
+
+fn main() {
+    rustc().input("depa.rs").run();
+    rustc().input("depb.rs").run();
+    rustc().input("depc.rs").run();
+    let output =
+        String::from_utf8(rustc().input("empty.rs").cfg("bar").command_output().stderr).unwrap();
+    let pos_a1 =
+        output.find("-ltesta").expect("empty.rs, compiled with --cfg, should contain -ltesta");
+    let pos_b = output[pos_a1..]
+        .find("-ltestb")
+        .map(|pos| pos + pos_a1)
+        .expect("empty.rs, compiled with --cfg, should contain -ltestb");
+    let _ = output[pos_b..]
+        .find("-ltesta")
+        .map(|pos| pos + pos_b)
+        .expect("empty.rs, compiled with --cfg, should contain a second -ltesta");
+    let output = String::from_utf8(rustc().input("empty.rs").command_output().stderr).unwrap();
+    assert!(output.contains("-ltesta"));
+    let output = String::from_utf8(rustc().input("empty.rs").command_output().stderr).unwrap();
+    assert!(!output.contains("-ltestb"));
+    let output = String::from_utf8(rustc().input("empty.rs").command_output().stderr).unwrap();
+    assert_eq!(output.matches("-ltesta").count, 1);
+}