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.

https://gitlab.freedesktop.org/NetworkManager/NetworkManager/issues/286

introspection/meson.build

@@ -56,6 +56,7 @@ ifaces = [
 ifaces_xmls = []
 sources = []
 introspection_files = []
+headers = []
 
 # FIXME?: DBUS_INTERFACE_DOCS/docbook files are generated in
 # "meson.current_build_dir()" instead of "meson.source_root()/docs/api"
@@ -85,6 +86,7 @@ foreach iface: ifaces
   # older versions
   if meson.version().version_compare('>= 0.46.0')
     introspection_files += [ [res[2], dbus_iface_xml_path] ]
+    headers += res[1]
   endif
 
 endforeach
@@ -102,9 +104,7 @@ libnmdbus = static_library(
 )
 
 libnmdbus_dep = declare_dependency(
-  # FIXME: only headers should be added here to resolve dependencies on
-  #        libNetworkManagerBase and libNetworkManager
-  #sources: sources,
+  sources: headers,
   include_directories: include_directories('.'),
   link_with: libnmdbus,
 )