Stack doesn't list optionally-compiled module in the targets

### General summary/comments (optional)
As @fendor pointed out in haskell/haskell-language-server#1270, it seems stack doesn't list modules which are turned off by default, but enabled by the flags configured in `stack.yaml`.

### Steps to reproduce

1. `git clone https://github.com/konn/hls-conditional-modules.git`
2. Run command `stack ghci`.

#### Include any `.yaml` configuration if relevant.
Included in the above repro repo, but the essential part is the following:

```yaml
flags:
hls-conditional-modules:
disable-lib2: false
```

### Expected

GHCi should load all four modules including `Lib2.hs` and `Lib2/Internal.hs`

### Actual

3. `Lib.hs` and `Lib/Internal.hs` are imported, but `Lib2.hs` and `Lib2/Internal.hs` aren't loaded which must be conditionally built.

This behaviour prevents HLS from loading necessary modules when some modules are off by default, as described in haskell/haskell-language-server#1270.

On the other hand, `stack build` builds all the needed modules based on the flags.

If you suspect that a stack command misbehaved, please include the output of that command in `--verbose` mode.
If the output is larger than a page please paste the output in a [Gist](https://gist.github.com/).

```$ stack ghci --verbose```

Gist: https://gist.github.com/konn/dd708b4623ef5f0ae8cf56905a7dedd5#file-stack-verbose-log

### Stack version

```
$ stack --version
Version 2.5.1, Git revision d6ab861544918185236cf826cb2028abb266d6d5 x86_64 hpack-0.33.0
```

### Method of installation

* Official binary, downloaded from stackage.org or fpcomplete's package repository and then upgraded by itself.