Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-4.0-pull-request...

Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-4.0-pull-request' into staging

fix gettid() clash with new glibc

# gpg: Signature made Mon 08 Apr 2019 20:36:06 BST
# gpg:                using RSA key F30C38BD3F2FBE3C
# 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-4.0-pull-request:
  linux-user: rename gettid() to sys_gettid() to avoid clash with glibc
  linux-user: assume __NR_gettid always exists

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