build: meson: fix dependency to gdbus generated headers

libnm has a dependency on 'libnmdbus_dep', which contains 'link_with:
libnmdbus'. This however only enforces that libnm is linked after the
libnmdbus static library is built; it doesn't give any guarantees
about the compilation phase.

We need to make libnm compilation depend on the generated header
files. The output of 'gnome.gdbus_codegen' is an array with the header
file in the second position; use it to add a proper
dependency. Unfortunately this works only with meson >= 0.46.

In the future libnm will no longer use gdbus generated code and this
dependency will not be needed anymore.

#286
19 jobs for bg/libnm-dbus-dep-issue286 in 91 minutes and 18 seconds (queued for 1 minute and 40 seconds)
latest
Status Job ID Name Coverage
  Test
passed #977209
allowed to fail
checkpatch

00:01:07

manual #977215
allowed to fail manual
t_centos:7.5.1804
passed #977216
t_centos:7.6.1810

00:21:34

passed #977222
t_debian:10

00:13:25

passed #977221
t_debian:9

00:14:05

passed #977224
t_debian:sid

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manual #977223
allowed to fail manual
t_debian:testing
manual #977210
allowed to fail manual
t_fedora:28
passed #977211
t_fedora:29

00:30:50

passed #977212
t_fedora:30

00:24:32

passed #977213
t_fedora:31

00:22:22

manual #977214
allowed to fail manual
t_fedora:rawhide
passed #982814
t_ubuntu:16.04

00:24:02

passed #977218
t_ubuntu:18.04

00:15:42

manual #977220
allowed to fail manual
t_ubuntu:devel
manual #977219
allowed to fail manual
t_ubuntu:rolling
failed #977217
t_ubuntu:16.04

01:17:18

 
  External
failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-code-upstream/890/

failed https://desktopqe-jenkins.rhev-ci-vms.eng.rdu2.redhat.com/job/beaker-NetworkManager-gitlab-trigger-code-upstream/890/

05:06:04