--wrap-mode ignores git submodules

Hey!

Running `meson setup ./foo` unconditionally updates any git-submodules that are used as subproject. This even ignores `--wrap-mode`. The code-base even mentions this:

```
# Note that these options do not affect subprojects that
# are git submodules since those are only usable in git
# repositories, and you almost always want to download them.
```

The only way to avoid this is to build _outside_ of a git checkout. This seems counter-intuitive, and counter-productive when developing applications. It is impossible to make meson build the current source with local modifications. Meson unconditionally updates the subprojects in this case (even ignoring the fact that it fetches from external servers for that).

Is there any way to make meson build a local git-checkout including its submodules without accessing the internet, and without modifying the source? Is there a rationale behind `--wrap-mode` ignoring git-submodules?

Fortunately, this only happens on `meson setup` invocation, so most developers will not trigger this when just rebuilding local modifications via `ninja`. However, if those local modifications require rebuilding the meson files, this issue will always be triggered.

Thanks!