Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-3.1-pull-request' into staging

This pull-request includes pre-requisite patches for the
"split do_syscall()" series. As they are clean-up, we can already
merge them.

# gpg: Signature made Wed 22 Aug 2018 02:12:08 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-3.1-pull-request:
  linux-user: Propagate goto fail to return
  linux-user: Propagate goto unimplemented to default
  linux-user: Propagate goto unimplemented_nowarn to return
  linux-user: Propagate goto efault to return
  linux-user: Relax single exit from "break"
  linux-user: Split out do_syscall1
  linux-user: Remove DEBUG

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