vars: Use uname() for architecture autodetection

[m-blaha]

The %_host_cpu macro is not runtime detected, it's only usable to detect
which architecture rpm was built for.
To detect that dnf5 is running on 32bit personality on x86_64 we need to
use uname().
The code is taken from libdnf (see libdnf/hy-util.cpp).

Resolves: https://bugzilla.redhat.com/show_bug.cgi?id=2252671

[j-mracek]

I believe that we can modify init_lib_rpm(arch); call. It was required to call it prior arch detection, but the new implementation does not require it. I would suggest to call it after the last step of detection is performed.

[m-blaha]

I believe that we can modify init_lib_rpm(arch); call. It was required to call it prior arch detection, but the new implementation does not require it. I would suggest to call it after the last step of detection is performed.

I've moved librpm initialization after arch detection.

[j-mracek]

LGTM, There are some failing tests, but it looks like that two PRs were somehow mixed -> ready to merge

[praiskup]

Awesome. Any ETA for when this will be added to F40 (Rawhide) repos? In particular this is blocking https://fedoraproject.org/wiki/Changes/BuildWithDNF5

[praiskup]

FTR, I tested with:

$ cat /tmp/test.cfg
include('/etc/mock/fedora-rawhide-i386.cfg')

config_opts['root'] = 'packit-rpm-software-management-dnf5-1063_fedora-rawhide-i386'
config_opts['isolation'] = 'unchanged'

config_opts["package_manager"] = 'dnf5'

config_opts['dnf.conf'] += """
[copr_base]
name="Copr repository"
baseurl=https://download.copr.fedorainfracloud.org/results/packit/rpm-software-management-dnf5-1063/fedora-rawhide-x86_64/
gpgcheck=0
enabled=1
skip_if_unavailable=1
metadata_expire=0
cost=1
best=1
"""

$ mock -r /tmp/test.cfg /home/praiskup/rh/packages/tar/fedora/tar-1.35-2.src.rpm
...

And it behaves as expected.