Auto merge of #94468 - Amanieu:global_asm_sym, r=nagisa

Implement sym operands for global_asm!

Tracking issue: #93333

This PR is pretty much a complete rewrite of `sym` operand support for inline assembly so that the same implementation can be shared by `asm!` and `global_asm!`. The main changes are:
- At the AST level, `sym` is represented as a special `InlineAsmSym` AST node containing a path instead of an `Expr`.
- At the HIR level, `sym` is split into `SymStatic` and `SymFn` depending on whether the path resolves to a static during AST lowering (defaults to `SynFn` if `get_early_res` fails).
  - `SymFn` is just an `AnonConst`. It runs through typeck and we just collect the resulting type at the end. An error is emitted if the type is not a `FnDef`.
  - `SymStatic` directly holds a path and the `DefId` of the `static` that it is pointing to.
- The representation at the MIR level is mostly unchanged. There is a minor change to THIR where `SymFn` is a constant instead of an expression.
- At the codegen level we need to apply the target's symbol mangling to the result of `tcx.symbol_name()` depending on the target. This is done by calling the LLVM name mangler, which handles all of the details.
  - On Mach-O, all symbols have a leading underscore.
  - On x86 Windows, different mangling is used for cdecl, stdcall, fastcall and vectorcall.
  - No mangling is needed on other platforms.

r? `@nagisa`
cc `@eddyb`

clippy_lints/src/loops/never_loop.rs

@@ -169,13 +169,14 @@ fn never_loop_expr(expr: &Expr<'_>, main_loop_id: HirId) -> NeverLoopResult {
             .iter()
             .map(|(o, _)| match o {
                 InlineAsmOperand::In { expr, .. }
-                | InlineAsmOperand::InOut { expr, .. }
-                | InlineAsmOperand::Sym { expr } => never_loop_expr(expr, main_loop_id),
+                | InlineAsmOperand::InOut { expr, .. } => never_loop_expr(expr, main_loop_id),
                 InlineAsmOperand::Out { expr, .. } => never_loop_expr_all(&mut expr.iter(), main_loop_id),
                 InlineAsmOperand::SplitInOut { in_expr, out_expr, .. } => {
                     never_loop_expr_all(&mut once(in_expr).chain(out_expr.iter()), main_loop_id)
                 },
-                InlineAsmOperand::Const { .. } => NeverLoopResult::Otherwise,
+                InlineAsmOperand::Const { .. }
+                | InlineAsmOperand::SymFn { .. }
+                | InlineAsmOperand::SymStatic { .. } => NeverLoopResult::Otherwise,
             })
             .fold(NeverLoopResult::Otherwise, combine_both),
         ExprKind::Struct(_, _, None)