Add codegen option for branch protection and pointer authentication on AArch64

The branch-protection codegen option enables the use of hint-space pointer
authentication code for AArch64 targets

src/test/codegen/branch-protection.rs

@@ -0,0 +1,41 @@
+// Test that the correct module flags are emitted with different branch protection flags.
+
+// revisions: bti pac-ret leaf b-key
+// min-llvm-version: 12.0.0
+// needs-llvm-components: aarch64
+// [bti] compile-flags: -C branch-protection=bti
+// [pac-ret] compile-flags: -C branch-protection=pac-ret
+// [leaf] compile-flags: -C branch-protection=pac-ret+leaf
+// [b-key] compile-flags: -C branch-protection=pac-ret+b-key
+// compile-flags: --target aarch64-unknown-linux-gnu
+
+#![crate_type = "lib"]
+#![feature(no_core, lang_items)]
+#![no_core]
+
+#[lang="sized"]
+trait Sized { }
+
+// A basic test function.
+pub fn test() {
+}
+
+// bti: !"branch-target-enforcement", i32 1
+// bti: !"sign-return-address", i32 0
+// bti: !"sign-return-address-all", i32 0
+// bti: !"sign-return-address-with-bkey", i32 0
+
+// pac-ret: !"branch-target-enforcement", i32 0
+// pac-ret: !"sign-return-address", i32 1
+// pac-ret: !"sign-return-address-all", i32 0
+// pac-ret: !"sign-return-address-with-bkey", i32 0
+
+// leaf: !"branch-target-enforcement", i32 0
+// leaf: !"sign-return-address", i32 1
+// leaf: !"sign-return-address-all", i32 1
+// leaf: !"sign-return-address-with-bkey", i32 0
+
+// b-key: !"branch-target-enforcement", i32 0
+// b-key: !"sign-return-address", i32 1
+// b-key: !"sign-return-address-all", i32 0
+// b-key: !"sign-return-address-with-bkey", i32 1