meson: build chardev trace files when have_block

The QSD depends on chardev code, and is built when have_tools is
true. This means conditionalizing chardev trace on have_system
is wrong, we need have_block which is set have_system || have_tools.

This latent bug was historically harmless because only the spice
chardev included tracing, which wasn't built in a !have_system
scenario.

Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Signed-off-by: Daniel P. Berrangé <berrange@redhat.com>

meson.build

@@ -3343,6 +3343,7 @@ if have_block
   trace_events_subdirs += [
     'authz',
     'block',
+    'chardev',
     'io',
     'nbd',
     'scsi',
@@ -3354,7 +3355,6 @@ if have_system
     'audio',
     'backends',
     'backends/tpm',
-    'chardev',
     'ebpf',
     'hw/9pfs',
     'hw/acpi',