Fix ICE when naked_asm uses const pointer operands

[0xmuon]

Fixes #1690
when naked_asm! uses a ptr valued const operand like const &0, codegen goes through global_asm and used to hit an unreachable!() on GlobalAlloc::Memory so the compiler ICE’d instead of emitting anything useful.This change handles those memory allocations the same way inline asm already does (via data_id_for_alloc_id) wire GlobalAsmContext up with the module and constants context it needs and turns unsupported allocation kinds into proper errors instead of panicking.