W32 Docker build fails
Description of problem:
Docker build fails:

```
make docker-test-mingw@fedora-win64-cross V=1 J=4
```

with the following error:

```
Initialized empty Git repository in /tmp/qemu-test/src/subprojects/dtc/.git/
fatal: unable to access 'https://gitlab.com/qemu-project/dtc.git/': Could not resolve host: gitlab.com

../meson.build:2090:16: ERROR: Git command failed: ['/usr/bin/git', 'fetch', '--depth', '1', 'origin', 'b6910bec11614980a21e46fbccc35934b671bd81']
```
Steps to reproduce:
1. `make docker-test-mingw@fedora-win64-cross V=1 J=4 DEBUG=1`
2. `cd $QEMU_SRC`
3. `mkdir build`
4. `cd build`
5. `../configure --cross-prefix=x86_64-w64-mingw32-`
Additional information:
The problem can be worked around by changing the line

```
subprojects="keycodemapdb libvfio-user berkeley-softfloat-3 berkeley-testfloat-3"
```

to

```
subprojects="keycodemapdb libvfio-user berkeley-softfloat-3 berkeley-testfloat-3 dtc"
```

in `archive-source.sh`.

Additionally, https://wiki.qemu.org/Hosts/W32#Docker_based_cross_builds is outdated.
```
make docker-test-mingw@fedora V=1 DEBUG=1 J=4
```
should be
```
make docker-test-mingw@fedora-win64-cross V=1 DEBUG=1 J=4
```

Additionally, i would suggest to create and enter build directory before calling configure and also add the make commands as shown in the "Steps to reproduce" section of this ticket.