libsereal-encoder-perl exclude s390x until it is fixed

[Alex Mestiashvili <alex@biotec.tu-dresden.de>]

Hi All,

libsereal-encoder-perl FTBFS on s390x - see for details #742409.

Can I exclude s390x from architectures for libsereal-encoder-perl until 
the problem is resolved ?
There is a number of packages which depend on it and which I really want 
to see in Jessie.

For example:
https://release.debian.org/migration/testing.pl?package=libdancer-session-cookie-perl

Thank you,
Alex