Update tests to use llvm_asm!

Author: Amanieu

src/librustc_error_codes/error_codes/E0668.md

@@ -7,7 +7,7 @@ assembly call.
 In particular, it can happen if you forgot the closing bracket of a register
 constraint (see issue #51430):
 ```compile_fail,E0668
-#![feature(asm)]
+#![feature(llvm_asm)]
 
 fn main() {
     let rax: u64;

src/test/codegen/no-output-asm-is-volatile.rs

@@ -1,6 +1,6 @@
 // compile-flags: -O
 
-#![feature(asm)]
+#![feature(llvm_asm)]
 #![crate_type = "lib"]
 
 // Check that inline assembly expressions without any outputs
@@ -9,6 +9,6 @@
 // CHECK-LABEL: @assembly
 #[no_mangle]
 pub fn assembly() {
-    unsafe { asm!("") }
+    unsafe { llvm_asm!("") }
 // CHECK: tail call void asm sideeffect "", {{.*}}
 }