math/big: Int.Lsh gives wrong results on s390x for n>=128 [1.15 backport] #45335
Description
@FiloSottile requested issue #42838 to be considered for backport to the next 1.15 minor release.
@gopherbot please backport to Go 1.15. This was included in the latest release, but remains an issue without workaround in the previous one.