Rewrite `link-arg` in rmake.rs

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -109,7 +109,6 @@ run-make/libtest-json/Makefile
 run-make/libtest-junit/Makefile
 run-make/libtest-padding/Makefile
 run-make/libtest-thread-limit/Makefile
-run-make/link-arg/Makefile
 run-make/link-args-order/Makefile
 run-make/link-cfg/Makefile
 run-make/link-dedup/Makefile

tests/run-make/link-arg/Makefile

@@ -1,5 +0,0 @@
-include ../tools.mk
-RUSTC_FLAGS = -C link-arg="-lfoo" -C link-arg="-lbar" --print link-args
-
-all:
-	$(RUSTC) $(RUSTC_FLAGS) empty.rs | $(CGREP) lfoo lbar

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

@@ -0,0 +1,24 @@
+// In 2016, the rustc flag "-C link-arg" was introduced - it can be repeatedly used
+// to add single arguments to the linker. This test passes 2 arguments to the linker using it,
+// then checks that the compiler's output contains the arguments passed to it.
+// This ensures that the compiler successfully parses this flag.
+// See https://github.com/rust-lang/rust/pull/36574
+
+use run_make_support::rustc;
+
+fn main() {
+    let output = String::from_utf8(
+        rustc()
+            .input("empty.rs")
+            .link_arg("-lfoo")
+            .link_arg("-lbar")
+            .print("link-args")
+            .command_output()
+            .stdout,
+    )
+    .unwrap();
+    assert!(
+        output.contains("lfoo") || output.contains("lbar"),
+        "The output did not contain the expected \"lfoo\" or \"lbar\" strings."
+    );
+}