proj-data cannot be installed in a cross-compiling scenario

[Yuri Astrakhan]

As reported at OSGeo/PROJ-data [1] and also found on stackexchange 5 years
ago [2], it seems it is not possible to install libproj9 in a
cross-compilation scenario:

[1] https://github.com/OSGeo/PROJ-data/issues/94
[2]
https://askubuntu.com/questions/997277/multiarch-issue-with-packages-marked-as-supporting-all-architectures

When using proj in a multi-architecture environment (compiling
cross-platform), the `proj-data` debian package does not exist.  The
stackexchange post [2] has some hacky solutions on how to get around this
issue.  I was trying to use https://github.com/cross-rs/cross 's docker
image, and inside install proj with:

`docker run --rm -it ghcr.io/cross-rs/aarch64-unknown-linux-gnu:latest`

```bash
dpkg --add-architecture arm64
apt-get update

apt show libproj9:arm64
# shows     Depends: proj-data, libc6 (>= 2.17)

apt-get install -y libproj9:arm64
# The following packages have unmet dependencies:
#  libproj9:arm64 : Depends: proj-data:arm64 but it is not installable

apt-get install -y proj-data:arm64
# E: Package 'proj-data:arm64' has no installation candidate
```

Thanks!
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