meson: Require XDR for wireshark

The way our wireshark dissector works is by providing decoders
for primitive types (like integers, string, double, etc.) and
then parsing virsomethingprotocol.x files and generating complex
decoders for RPC. This obviously means that XDR is required for
the dissector, but corresponding check was missing.

Signed-off-by: Michal Privoznik <mprivozn@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>

meson.build

@@ -1310,6 +1310,16 @@ endif
 
 wireshark_version = '2.6.0'
 wireshark_dep = dependency('wireshark', version: '>=' + wireshark_version, required: get_option('wireshark_dissector'))
+if wireshark_dep.found()
+  if not xdr_dep.found()
+    if get_option('wireshark_dissector').enabled()
+      error('XDR is required for wireshark plugin')
+    else
+      wireshark_dep = dependency('', required: false)
+    endif
+  endif
+endif
+
 if wireshark_dep.found()
   wireshark_plugindir = get_option('wireshark_plugindir')
   if wireshark_plugindir == ''