Full asm!() support

• Support const operands.
  • For inline asm (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1350)
  • For global asm (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1351)
• Support sym operands.
  • For inline asm (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1350)
  • For global asm (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1351, but doesn't work when the function is made private to the codegen unit)
  • Missing symbol mangling (_ prefix for Mach-O) (https://github.com/rust-lang/rustc_codegen_cranelift/pull/1630)
• Support asm goto (https://github.com/rust-lang/rust/pull/133870 will stabilize it for cg_llvm)
• Support register classes. This will require writing a mini register allocator to solve all register constraints. (#1206)
• Optimize
  • Overlap input and output stack slots. (#1206)
  • Skip saving caller saved registers. (#1206)
• Support more architectures
  • aarch64 (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1396)
  • riscv64 (https://github.com/rust-lang/rustc_codegen_cranelift/pull/1398)
  • ...
• Support inline asm on macOS (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1397)
• Support inline asm on Windows (https://github.com/rust-lang/rustc_codegen_cranelift/pull/1403)
• Avoid the object file linking hack. It doesn't work on macOS and Windows but is currently necessary as incr comp expects each codegen unit to provide a single object file instead of allowing an extra object file for the compiled assembly. (#1264)
• Use cgu name instead of function name as base for assembly stub names. The same function name may be used in multiple cgus when using #[inline]. (122219237437ee1deee33df9806a4316194a6f76)
• Run inline asm tests from the rustc test suite (https://github.com/bjorn3/rustc_codegen_cranelift/pull/1397)
• Enable support by default (https://github.com/rust-lang/rustc_codegen_cranelift/pull/1403)

Tracking issue for stabilizing asm!(): https://github.com/rust-lang/rust/issues/72016 Has been stabilized.

Review the unchecked checklist items, starting with the global sym operand limitation described alongside PR 1351 and the asm goto work linked to rust-lang/rust#133870. Compare the backend's current status with those references and identify the remaining architecture gaps. Done means the outstanding checklist items are implemented and the tracking issue is updated.