Merge remote-tracking branch 'remotes/vivier2/tags/linux-user-for-5.2-pull-request' into staging

Add ppoll_time64() and pselect6_time64()
Some fixes for for elfload, fcntl, termbits and btrfs

# gpg: Signature made Mon 07 Sep 2020 10:17:24 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-5.2-pull-request:
  linux-user: Protect btrfs ioctl target definitions
  linux-user: fix ppc/termbits.h
  linux-user: Map signal numbers in fcntl
  linux-user: Correctly start brk after executable
  linux-user: Add support for ppoll_time64() and pselect6_time64()

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