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`

compiler/rustc_hir/src/hir.rs

@@ -2425,8 +2425,12 @@ pub enum InlineAsmOperand<'hir> {
     Const {
         anon_const: AnonConst,
     },
-    Sym {
-        expr: Expr<'hir>,
+    SymFn {
+        anon_const: AnonConst,
+    },
+    SymStatic {
+        path: QPath<'hir>,
+        def_id: DefId,
     },
 }
 
@@ -2437,7 +2441,7 @@ impl<'hir> InlineAsmOperand<'hir> {
             | Self::Out { reg, .. }
             | Self::InOut { reg, .. }
             | Self::SplitInOut { reg, .. } => Some(reg),
-            Self::Const { .. } | Self::Sym { .. } => None,
+            Self::Const { .. } | Self::SymFn { .. } | Self::SymStatic { .. } => None,
         }
     }