v8a as default aarch64 target

After llvm/llvm-project@8689f5e landed, LLVM takes the intersection of v8a and v8r as default.
This commit brings back v8a support by explicitly specifying v8a in the feature list.

This should solve #97724.

compiler/rustc_codegen_llvm/src/llvm_util.rs

@@ -491,6 +491,11 @@ pub(crate) fn global_llvm_features(sess: &Session, diagnostics: bool) -> Vec<Str
         .flatten();
     features.extend(feats);
 
+    // FIXME: Move v8a to target definition list when earliest supported LLVM is 14.
+    if get_version() >= (14, 0, 0) && sess.target.arch == "aarch64" {
+        features.push("+v8a".into());
+    }
+
     if diagnostics && let Some(f) = check_tied_features(sess, &featsmap) {
         sess.emit_err(TargetFeatureDisableOrEnable {
             features: f,

src/test/assembly/asm/aarch64-el2vmsa.rs

@@ -0,0 +1,37 @@
+// assembly-output: emit-asm
+// compile-flags: --target aarch64-unknown-linux-gnu
+// needs-llvm-components: aarch64
+
+#![feature(no_core, lang_items, rustc_attrs)]
+#![crate_type = "rlib"]
+#![no_core]
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+    () => {};
+}
+
+#[lang = "sized"]
+trait Sized {}
+
+// CHECK-LABEL: ttbr0_el2:
+#[no_mangle]
+pub fn ttbr0_el2() {
+    // CHECK: //APP
+    // CHECK-NEXT: msr TTBR0_EL2, x0
+    // CHECK-NEXT: //NO_APP
+    unsafe {
+        asm!("msr ttbr0_el2, x0");
+    }
+}
+
+// CHECK-LABEL: vttbr_el2:
+#[no_mangle]
+pub fn vttbr_el2() {
+    // CHECK: //APP
+    // CHECK-NEXT: msr VTTBR_EL2, x0
+    // CHECK-NEXT: //NO_APP
+    unsafe {
+        asm!("msr vttbr_el2, x0");
+    }
+}