cmd/objdump: implement s390x disassembler

[mundaym]

Unplanned at the moment.

[gopherbot]

CL https://golang.org/cl/21894 mentions this issue.

[srinivas-pokala]

@rsc, I am working on disassembler support for linux/s390x

[gopherbot]

Change https://go.dev/cl/575735 mentions this issue: cmd/objdump: implement s390x go disassembler support

[gopherbot]

Change https://go.dev/cl/579977 mentions this issue: cmd/objdump: enable disassembler tests on s390x platform

[gopherbot]

Change https://go.dev/cl/581015 mentions this issue: cmd/vendor/golang.org/x/arch:add s390x disassembler changes

[Vishwanatha-HD]

The s390x disassembler support CL# is (arch repo):
https://go-review.googlesource.com/c/arch/+/575675