cmd/compile: use | in the most repetitive s390x rules

cmd/compile: use | in the most repetitive s390x rules

For now, limited to the most repetitive rules that are also short and
simple, so that we can have a substantial conciseness win without
compromising rules readability.

Ran rulegen, no changes in the rewrite files.

Change-Id: I8447784895a218c5c1b4dfa1cdb355bd73dabfd1
Reviewed-on: https://go-review.googlesource.com/95955
Reviewed-by: Giovanni Bajo <rasky@develer.com>