Add deferred logic for BUILD_DEPENDS

[scaronni]

Add deferred logic for BUILD_DEPENDS with multiple package upgrades (kernel, modules and dependent modules) when invoking autoinstall.

The issue

Practical issue in Ubuntu:

1. Module with a dependency specified:

$ cat /usr/src/nvidia-fs-2.26.6/dkms.conf | grep BUILD_DEPENDS
BUILD_DEPENDS[0]="nvidia"

2. A transaction involving an update of the kernel and the nvidia DKMS module at the same time:

Autoinstall on 6.14.0-1011-nvidia-64k succeeded for module(s) kernel-mft-dkms knem mlnx-ofed-kernel xpmem.
nvidia-fs/2.26.6 autoinstall failed due to missing dependencies: nvidia.

Error! One or more modules failed to install during autoinstall.
Refer to previous errors for more information.
run-parts: /etc/kernel/header_postinst.d/dkms exited with return code 1
dpkg: error processing package linux-headers-6.14.0-1011-nvidia-64k (--configure):
 installed linux-headers-6.14.0-1011-nvidia-64k package post-installation script subprocess returned error exit status 1

3. At the end of the upgrade, DKMS triggers a rebuild of nvidia-fs, which now succeeds because the nvidia module has now been built:

Autoinstall of module nvidia-fs/2.26.6 for kernel 6.14.0-1011-nvidia-64k (aarch64)
Building module(s).......... done.
Signing module /var/lib/dkms/nvidia-fs/2.26.6/build/nvidia-fs.ko
Found pre-existing /lib/modules/6.14.0-1011-nvidia-64k/ubuntu/nvidia-fs/nvidia-fs.ko.zst, archiving for uninstallation
Installing /lib/modules/6.14.0-1011-nvidia-64k/updates/dkms/nvidia-fs.ko.zst
Running depmod... done.

Autoinstall on 6.14.0-1011-nvidia-64k succeeded for module(s) iser isert kernel-mft-dkms knem mlnx-nfsrdma mlnx-nvme mlnx-ofed-kernel nvidia srp xpmem nvidia-fs.

But at this point, the initial failure causes the apt transaction to report a failure:

Errors were encountered while processing:
 linux-headers-6.14.0-1011-nvidia-64k
 linux-headers-nvidia-64k-6.14
 linux-nvidia-64k-6.14

Deferred logic for hard dependencies

autoinstall now distinguishes two kinds of unresolved BUILD_DEPENDS (taken from the comments in dkms.in):

• "real" missing dependency:
  The dependency is a DKMS-managed module (in known_modules) that we tried but could not install (e.g. circular dependency, build failure of the dependency).

• "deferred" missing dependency:
  The dependency is not registered with DKMS at all. This commonly happens during multi-package installs where the dependency's source package has not yet been configured by dpkg/rpm, so its postinst hasn't run dkms add yet. The dependency may also be supplied by something outside DKMS entirely. Either way, the current autoinstall run cannot make progress on it, but a later trigger (the dependency package's own postinst, or a re-run of this hook) will. Don't fail the whole transaction in that case.

By running dkms build directly, as it was before, exit 13 is still returned unless --force is used. The relaxation (the deferred logic) is only on the automated path where DKMS doesn't have full visibility into pending package operations.

[amilonenv]

It looks good to me.