tests: Test pac-ret flag merging on clang with LTO

Extend the test for pac-ret with clang and LTO by checking that
different branch protection flags are preserved after the LTO step.
There was an issue in older LLVM versions that was causing this to
behave incorrectly.

Tests the LLVM behaviour added in:
https://github.com/llvm/llvm-project/commit/1782810b8440144a0141c24192acbaeb55a1545d

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

@@ -10,14 +10,16 @@
 //@ ignore-cross-compile
 // Reason: the compiled binary is executed
 
-use run_make_support::{clang, env_var, llvm_ar, run, rustc, static_lib_name};
+use run_make_support::{clang, env_var, llvm_ar, llvm_objdump, run, rustc, static_lib_name};
+
+static PAUTH_A_KEY_PATTERN: &'static str = "paciasp";
+static PAUTH_B_KEY_PATTERN: &'static str = "pacibsp";
 
 fn main() {
     clang()
         .arg("-v")
         .lto("thin")
-        .arg("-mbranch-protection=bti+pac-ret+leaf")
-        .arg("-O2")
+        .arg("-mbranch-protection=bti+pac-ret+b-key+leaf")
         .arg("-c")
         .out_exe("test.o")
         .input("test.c")
@@ -32,5 +34,15 @@ fn main() {
         .input("test.rs")
         .output("test.bin")
         .run();
+
+    // Check that both a-key and b-key pac-ret survived LTO
+    llvm_objdump()
+        .disassemble()
+        .input("test.bin")
+        .run()
+        .assert_stdout_contains_regex(PAUTH_A_KEY_PATTERN)
+        .assert_stdout_contains_regex(PAUTH_B_KEY_PATTERN);
+
+    // Check that the binary actually runs
     run("test.bin");
 }