disallow asm! in #[naked] functions

also disallow the `noreturn` option, and infer `naked_asm!` as `!`

core/src/arch.rs

@@ -77,17 +77,3 @@ pub macro naked_asm("assembly template", $(operands,)* $(options($(option),*))?)
 pub macro global_asm("assembly template", $(operands,)* $(options($(option),*))?) {
     /* compiler built-in */
 }
-
-/// Inline assembly used in combination with `#[naked]` functions.
-///
-/// Refer to [Rust By Example] for a usage guide and the [reference] for
-/// detailed information about the syntax and available options.
-///
-/// [Rust By Example]: https://doc.rust-lang.org/nightly/rust-by-example/unsafe/asm.html
-/// [reference]: https://doc.rust-lang.org/nightly/reference/inline-assembly.html
-#[unstable(feature = "naked_functions", issue = "90957")]
-#[rustc_builtin_macro]
-#[cfg(not(bootstrap))]
-pub macro naked_asm("assembly template", $(operands,)* $(options($(option),*))?) {
-    /* compiler built-in */
-}