Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-3.0-pull-request...

Sanitize linux-user stdout

# gpg: Signature made Tue 10 Jul 2018 07:23:34 BST
# gpg:                using RSA key F30C38BD3F2FBE3C
# gpg: Good signature from "Laurent Vivier <lvivier@redhat.com>"
# gpg:                 aka "Laurent Vivier <laurent@vivier.eu>"
# gpg:                 aka "Laurent Vivier (Red Hat) <lvivier@redhat.com>"
# Primary key fingerprint: CD2F 75DD C8E3 A4DC 2E4F  5173 F30C 38BD 3F2F BE3C

* remotes/vivier2/tags/linux-user-for-3.0-pull-request:
  linux-user: Report error message on stderr, rather than stdout
  linux-user: Do not report "syscall not implemented" by default
  linux-user: Do not report "Unsupported syscall" by default

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