Add test for issue 99071

Author: Amanieu

src/test/ui/asm/issue-99071.rs

@@ -0,0 +1,21 @@
+// compile-flags: --target thumbv6m-none-eabi
+// needs-llvm-components: arm
+// needs-asm-support
+
+#![feature(no_core, lang_items, rustc_attrs)]
+#![no_core]
+#![crate_type = "rlib"]
+
+#[rustc_builtin_macro]
+macro_rules! asm {
+    () => {};
+}
+#[lang = "sized"]
+trait Sized {}
+
+pub fn foo() {
+    unsafe {
+        asm!("", in("r8") 0);
+        //~^ cannot use register `r8`: high registers (r8+) can only be used as clobbers in Thumb-1 code
+    }
+}

src/test/ui/asm/issue-99071.stderr

@@ -0,0 +1,8 @@
+error: cannot use register `r8`: high registers (r8+) can only be used as clobbers in Thumb-1 code
+  --> $DIR/issue-99071.rs:18:18
+   |
+LL |         asm!("", in("r8") 0);
+   |                  ^^^^^^^^^^
+
+error: aborting due to previous error
+