parseAsmInputItem

fn parseAsmInputItem(p: *Parse) !?Node.Index {
    _ = p.eatToken(.l_bracket) orelse return null;
    const identifier = try p.expectToken(.identifier);
    _ = try p.expectToken(.r_bracket);
    _ = try p.expectToken(.string_literal);
    _ = try p.expectToken(.l_paren);
    const expr = try p.expectExpr();
    const rparen = try p.expectToken(.r_paren);
    return try p.addNode(.{
        .tag = .asm_input,
        .main_token = identifier,
        .data = .{ .node_and_token = .{
            expr,
            rparen,
        } },
    });
}