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_codegen_llvm/src/llvm/ffi.rs

@@ -1616,6 +1616,20 @@ extern "C" {
         Name: *const c_char,
     ) -> &'a Value;
 
+    pub fn LLVMRustBuildCallBr<'a>(
+        B: &Builder<'a>,
+        Ty: &'a Type,
+        Fn: &'a Value,
+        DefaultDest: &'a BasicBlock,
+        IndirectDests: *const &'a BasicBlock,
+        NumIndirectDests: c_uint,
+        Args: *const &'a Value,
+        NumArgs: c_uint,
+        OpBundles: *const &OperandBundleDef<'a>,
+        NumOpBundles: c_uint,
+        Name: *const c_char,
+    ) -> &'a Value;
+
     pub fn LLVMRustSetFastMath(Instr: &Value);
     pub fn LLVMRustSetAlgebraicMath(Instr: &Value);
     pub fn LLVMRustSetAllowReassoc(Instr: &Value);