Stabilize asm_goto feature gate

[nbdd0121]

Stabilize asm_goto feature (tracked by #119364). The issue will remain open and be updated to track asm_goto_with_outputs.

Reference PR: rust-lang/reference#1693

Stabilization Report

This feature adds a label <block> operand type to asm!. <block> must be a block expression with type unit or never. The address of the block is substituted and the assembly may jump to the block. When block completes the asm! block returns and continues execution.

The block starts a new safety context and unsafe operations within must have additional unsafes; the effect of unsafe that surrounds asm! block is cancelled. See #119364 (comment) and #131544.

It's currently forbidden to use asm_goto with output operands; that is still unstable under asm_goto_with_outputs.

Example:

unsafe {
    asm!(
        "jmp {}",
        label {
            println!("Jumped from asm!");
        }
    );
}

Tests:

• tests/ui/asm/x86_64/goto.rs
• tests/ui/asm/x86_64/goto-block-safe.stderr
• tests/ui/asm/x86_64/bad-options.rs
• tests/codegen/asm/goto.rs

[rustbot]

r? @ehuss

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[nbdd0121]

@rustbot label: -T-compiler +T-lang +A-inline-assembly +F-asm

Cc @rust-lang/wg-inline-asm

[ehuss]

r? compiler

cc @Amanieu

[nnethercote]

The code changes look fine for stabilizing this feature, so r=me in terms of code. But I am uncertain about the stabilization process. Is any additional T-lang approval needed before this merges? Has such approval already been obtained?

[nbdd0121]

@nnethercote this would need a FCP.

[jieyouxu]

r? lang (for T-lang FCP)