tests: add pac-ret + cross-language lto test

Add a test confirming that `-Zbranch-protection=pac-ret` and
cross-language LTO work together.

Author: davidtwco

Diff for: tests/run-make/pointer-auth-link-with-c-lto-clang/rmake.rs

@@ -0,0 +1,36 @@
+// `-Z branch protection` is an unstable compiler feature which adds pointer-authentication
+// code (PAC), a useful hashing measure for verifying that pointers have not been modified.
+// This test checks that compilation and execution is successful when this feature is activated,
+// with some of its possible extra arguments (bti, pac-ret, leaf) when doing LTO.
+// See https://github.com/rust-lang/rust/pull/88354
+
+//@ needs-force-clang-based-tests
+//@ only-aarch64
+// Reason: branch protection is not supported on other architectures
+//@ ignore-cross-compile
+// Reason: the compiled binary is executed
+
+use run_make_support::{clang, env_var, llvm_ar, run, rustc, static_lib_name};
+
+fn main() {
+    clang()
+        .arg("-v")
+        .lto("thin")
+        .arg("-mbranch-protection=bti+pac-ret+leaf")
+        .arg("-O2")
+        .arg("-c")
+        .out_exe("test.o")
+        .input("test.c")
+        .run();
+    llvm_ar().obj_to_ar().output_input(static_lib_name("test"), "test.o").run();
+    rustc()
+        .linker_plugin_lto("on")
+        .opt_level("2")
+        .linker(&env_var("CLANG"))
+        .link_arg("-fuse-ld=lld")
+        .arg("-Zbranch-protection=bti,pac-ret,leaf")
+        .input("test.rs")
+        .output("test.bin")
+        .run();
+    run("test.bin");
+}

Diff for: tests/run-make/pointer-auth-link-with-c-lto-clang/test.c

@@ -0,0 +1 @@
+int foo() { return 0; }

Diff for: tests/run-make/pointer-auth-link-with-c-lto-clang/test.rs

@@ -0,0 +1,10 @@
+#[link(name = "test")]
+extern "C" {
+    fn foo() -> i32;
+}
+
+fn main() {
+    unsafe {
+        foo();
+    }
+}