Rollup merge of rust-lang#119365 - nbdd0121:asm-goto, r=Amanieu

Add asm goto support to `asm!`

Tracking issue: rust-lang#119364

This PR implements asm-goto support, using the syntax described in "future possibilities" section of [RFC2873](https://rust-lang.github.io/rfcs/2873-inline-asm.html#asm-goto).

Currently I have only implemented the `label` part, not the `fallthrough` part (i.e. fallthrough is implicit). This doesn't reduce the expressive though, since you can use label-break to get arbitrary control flow or simply set a value and rely on jump threading optimisation to get the desired control flow. I can add that later if deemed necessary.

r? ``@Amanieu``
cc ``@ojeda``

clippy_lints/src/loops/never_loop.rs

@@ -255,6 +255,9 @@ fn never_loop_expr<'tcx>(
             InlineAsmOperand::Const { .. } | InlineAsmOperand::SymFn { .. } | InlineAsmOperand::SymStatic { .. } => {
                 NeverLoopResult::Normal
             },
+            InlineAsmOperand::Label { block } => {
+                never_loop_block(cx, block, local_labels, main_loop_id)
+            }
         })),
         ExprKind::OffsetOf(_, _)
         | ExprKind::Yield(_, _)

clippy_utils/src/hir_utils.rs

@@ -833,6 +833,7 @@ impl<'a, 'tcx> SpanlessHash<'a, 'tcx> {
                             self.hash_body(anon_const.body);
                         },
                         InlineAsmOperand::SymStatic { path, def_id: _ } => self.hash_qpath(path),
+                        InlineAsmOperand::Label { block } => self.hash_block(block),
                     }
                 }
             },