Support using const pointers in asm const operand

[nbdd0121]

Implements #128464

This adds support of const pointers for asm const in addition to plain integers.

The inline asm! support is implemented using i constraint, and the global_asm! and naked_asm! support is implemented by inserting symbol + offset and make symbol compiler-used. For unnamed consts, it will create additional internal & hidden symbols so that they can be referenced by global_asm.

GCC impl is still WIP.

[rustbot]

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[fmease]

r? codegen

[rust-log-analyzer]

The job mingw-check failed! Check out the build log: (web) (plain)

Click to see the possible cause of the failure (guessed by this bot)

[RUSTC-TIMING] gccjit_sys test:false 0.024
    Checking gccjit v2.4.0
[RUSTC-TIMING] gccjit test:false 0.170
    Checking rustc_codegen_gcc v0.1.0 (/checkout/compiler/rustc_codegen_gcc)
error[E0004]: non-exhaustive patterns: `GlobalAsmOperandRef::ConstPointer { .. }` not covered
   --> compiler/rustc_codegen_gcc/src/asm.rs:853:27
    |
853 |                     match operands[operand_idx] {
    |                           ^^^^^^^^^^^^^^^^^^^^^ pattern `GlobalAsmOperandRef::ConstPointer { .. }` not covered
    |
note: `GlobalAsmOperandRef<'_>` defined here
   --> /checkout/compiler/rustc_codegen_ssa/src/traits/asm.rs:47:1
    |
47  | pub enum GlobalAsmOperandRef<'tcx> {

[compiler-errors]

r? compiler-errors