Check for llvm_asm in a const context

src/test/ui/consts/inline_asm.rs

@@ -0,0 +1,6 @@
+#![feature(llvm_asm)]
+
+const _: () = unsafe { llvm_asm!("nop") };
+//~^ ERROR contains unimplemented expression type
+
+fn main() {}

src/test/ui/consts/inline_asm.stderr

@@ -0,0 +1,9 @@
+error[E0019]: constant contains unimplemented expression type
+  --> $DIR/inline_asm.rs:3:1
+   |
+LL | const _: () = unsafe { llvm_asm!("nop") };
+   | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
+
+error: aborting due to previous error
+
+For more information about this error, try `rustc --explain E0019`.