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

Add asm goto support to `asm!`

Tracking issue: #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``

compiler/rustc_hir_analysis/src/check/intrinsicck.rs

@@ -470,6 +470,8 @@ impl<'a, 'tcx> InlineAsmCtxt<'a, 'tcx> {
                         }
                     };
                 }
+                // No special checking is needed for labels.
+                hir::InlineAsmOperand::Label { .. } => {}
             }
         }
     }