bug! if branch-protection makes it to non-AArch64 codegen.

Author: jacobbramley

compiler/rustc_codegen_llvm/src/context.rs

@@ -274,9 +274,8 @@ pub unsafe fn create_module<'ll>(
         }
     }
 
-    // AArch64-only options (checked in rustc_session).
-    if sess.target.arch == "aarch64" {
-        if let Some(BranchProtection { bti, pac_ret }) = sess.opts.unstable_opts.branch_protection {
+    if let Some(BranchProtection { bti, pac_ret }) = sess.opts.unstable_opts.branch_protection {
+        if sess.target.arch == "aarch64" {
             llvm::LLVMRustAddModuleFlag(
                 llmod,
                 llvm::LLVMModFlagBehavior::Error,
@@ -302,6 +301,11 @@ pub unsafe fn create_module<'ll>(
                 "sign-return-address-with-bkey\0".as_ptr().cast(),
                 u32::from(pac_opts.key == PAuthKey::B),
             );
+        } else {
+            bug!(
+                "branch-protection used on non-AArch64 target; \
+                  this should be checked in rustc_session."
+            );
         }
     }