False negative `Warning: Unreachable code.` in inline assembly

The code in [1] issues the warning in [2], which is not true since the function is called.

[1]
```solidity
contract C {
function f(uint) external pure returns (uint) {
assembly {
mstore(0, id(calldataload(4)))
return (0, 32)

function id(x) -> y {
y := x
}
}
}
}
```

[2]
```bash
Warning: Unreachable code.
--> contracts/3_Ballot.sol:7:13:
|
7 | function id(x) -> y {
| ^ (Relevant source part starts here and spans across multiple lines)
```