Migrate run-make/allow-warnings-cmdline-stability to rmake.rs

Author: GuillaumeGomez

src/tools/tidy/src/allowed_run_make_makefiles.txt

@@ -1,6 +1,5 @@
 run-make/allocator-shim-circular-deps/Makefile
 run-make/allow-non-lint-warnings-cmdline/Makefile
-run-make/allow-warnings-cmdline-stability/Makefile
 run-make/archive-duplicate-names/Makefile
 run-make/atomic-lock-free/Makefile
 run-make/bare-outfile/Makefile

tests/run-make/allow-warnings-cmdline-stability/Makefile

@@ -0,0 +1,11 @@
+// Test that `-Awarnings` suppresses warnings for unstable APIs.
+
+use run_make_support::{assert_not_contains, rustc};
+
+fn main() {
+    rustc().input("bar.rs").run();
+    let output = rustc().input("foo.rs").arg("-Awarnings").run();
+
+    assert_not_contains(&String::from_utf8(output.stdout).unwrap(), "warning");
+    assert_not_contains(&String::from_utf8(output.stderr).unwrap(), "warning");
+}