SSA CFG codegen emits library placeholders for internal libraries

## Description

The SSA CFG-based code generation sometimes emits library placeholders for internal libraries. This occurs only when using a non-standard yul optimization sequence (in this case the standard one without UnusedPruners (u) steps).

## Environment

- Compiler version: 0.8.35+commit.47b9dedd
- Compilation pipeline (legacy, IR, EOF): IR + experimental SSA CFG
- Target EVM version (as per compiler settings): osaka
- Framework/IDE (e.g. Foundry, Hardhat, Remix): NA
- EVM execution environment / backend / blockchain client: NA
- Operating system: macOS arm64 and linux x86-64

## Steps to Reproduce

**target.sol**
```solidity
pragma solidity ^0.8.35;

library L {
function f() internal returns (uint256) {
return 1;
}
}

contract N {
function p() external {}
}

contract PlaceholderContract {
function check_entrypoint() public {
(new N()).p();
assert(L.f() == 1);
}
}
```

**cli command (experimental w/ placeholder)**
```
solc --bin-runtime --optimize --optimize-runs 100 --via-ssa-cfg --experimental --evm-version osaka --yul-optimizations 'dhfoD[xarrscLMcCTU]ljml:fDnTOcm' target.sol
```

Produces bytecode containing a library placeholder. (not expected)

```
6080....5b73__$825ecdb7db853ecb5831abd3822386e16e$__61014...0041
```

**cli command (non experimental)**
```
solc --bin-runtime --optimize --optimize-runs 100 --evm-version osaka --yul-optimizations 'dhfoD[xarrscLMcCTU]ljml:fDnTOcm' target.sol
```

Produces bytecode without library placeholders. (expected)

## Expected Behavior

All functions in the library are marked as internal and should be embedded directly without needing to link to a library. The legacy compile pipeline as well as via-IR using the same compiler options do not emit library placeholders in this case.