Allow pointers in inline assembly `const` expressions

[dingxiangfei2009]

Quoting from tests/ui/asm/const-refs-to-static.rs @ 31e102c

I tried this code:

use std::arch::{asm, global_asm};
use std::ptr::addr_of;

static FOO: u8 = 42;

#[no_mangle]
fn inline() {
    unsafe { asm!("{}", const addr_of!(FOO)) };
}

I expected to see this happen: it should compiles

Instead, this happened: *const u8 is not allowed as an operand to inline assembly.

This would be coming useful and brings us feature-parity with asm(" /* assembly */ " ::"i"(ptr)) from C, where ptr can be pointer to statics and constants.

cc @Amanieu @nbdd0121

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[dingxiangfei2009]

I am trying a quick implementation on it.

@rustbot claim

[nbdd0121]

This was tracked by #128464 and I have been working on it for a couple of days now. While the codegen change needed was simple, the typeck/borrowck aspect of this was really non-trivial.

[dingxiangfei2009]

Thanks for pointing that out @nbdd0121 ! Is there a tracking issue for the string interpolating constraint in asm!? If not yet, I can create it.