So after da176bf6 and friend we have switched to $(wildcard
some/path/*.xml) instead of enumerating the files explicitly.
This is nice, however it makes distcheck build from VPATH fail.
The reason is that it's is not obvious to what does the wildcard
refer to: srcdir or builddir?
Signed-off-by: NMichal Privoznik <mprivozn@redhat.com>