Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-6.0-pull-request...

Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-6.0-pull-request' into staging

linux-user pull request 20210328

- Fix recvfrom with NULL msg
- Fix sigreturn address on s390x

# gpg: Signature made Sun 28 Mar 2021 17:05:45 BST
# gpg:                using RSA key CD2F75DDC8E3A4DC2E4F5173F30C38BD3F2FBE3C
# gpg:                issuer "laurent@vivier.eu"
# gpg: Good signature from "Laurent Vivier <lvivier@redhat.com>" [full]
# gpg:                 aka "Laurent Vivier <laurent@vivier.eu>" [full]
# gpg:                 aka "Laurent Vivier (Red Hat) <lvivier@redhat.com>" [full]
# Primary key fingerprint: CD2F 75DD C8E3 A4DC 2E4F  5173 F30C 38BD 3F2F BE3C

* remotes/vivier2/tags/linux-user-for-6.0-pull-request:
  linux-user: allow NULL msg in recvfrom
  linux-user/s390x: Use the guest pointer for the sigreturn stub

Signed-off-by: Peter Maydell <peter.maydell@linaro.org>