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_const_eval/src/interpret/machine.rs

@@ -374,11 +374,17 @@ pub trait Machine<'mir, 'tcx: 'mir>: Sized {
         kind: Option<MemoryKind<Self::MemoryKind>>,
     ) -> InterpResult<'tcx, Cow<'b, Allocation<Self::Provenance, Self::AllocExtra, Self::Bytes>>>;
 
+    /// Evaluate the inline assembly.
+    ///
+    /// This should take care of jumping to the next block (one of `targets`) when asm goto
+    /// is triggered, `targets[0]` when the assembly falls through, or diverge in case of
+    /// `InlineAsmOptions::NORETURN` being set.
     fn eval_inline_asm(
         _ecx: &mut InterpCx<'mir, 'tcx, Self>,
         _template: &'tcx [InlineAsmTemplatePiece],
         _operands: &[mir::InlineAsmOperand<'tcx>],
         _options: InlineAsmOptions,
+        _targets: &[mir::BasicBlock],
     ) -> InterpResult<'tcx> {
         throw_unsup_format!("inline assembly is not supported")
     }