64 bit zlib

Ever since I added s390x support to zlib the package has been failing to
build on the buildd, apparently because it doesn't support s390x
binaries.  This hasn't been a showstopper since the package seems to be
getting built somehow but it is a bit worrying seeing the failed build
report and will create more work for porters.  

Is there anything I can do to stop the build being tried on unsuitable
machines?

-- 
"You grabbed my hand and we fell into it, like a daydream - or a fever."