Merge remote-tracking branch 'remotes/xtensa/tags/20180402-xtensa' into staging

Merge remote-tracking branch 'remotes/xtensa/tags/20180402-xtensa' into staging

xtensa-specific fixes for linux-user:

- fix flushing registers for signal processing in call8 and call12 frames;
- fix PC value for restarted syscalls;
- fix sysv IPC structures;
- fix fadvise64 syscall;

generic fixes for linux-user:

- fix QEMU assertion in multithreaded application by calling cpu_copy
  under clone_lock;
- fix mq_getsetattr implementation;
- fix error propagation in clock_gettime;
- implement clock_settime.

# gpg: Signature made Mon 02 Apr 2018 18:07:08 BST
# gpg:                using RSA key 51F9CC91F83FA044
# gpg: Good signature from "Max Filippov <filippov@cadence.com>"
# gpg:                 aka "Max Filippov <max.filippov@cogentembedded.com>"
# gpg:                 aka "Max Filippov <jcmvbkbc@gmail.com>"
# Primary key fingerprint: 2B67 854B 98E5 327D CDEB  17D8 51F9 CC91 F83F A044

* remotes/xtensa/tags/20180402-xtensa:
  target/xtensa: linux-user: fix fadvise64 call
  linux-user: implement clock_settime
  linux-user: fix error propagation in clock_gettime
  target/xtensa: linux-user: fix sysv IPC structures
  linux-user: fix mq_getsetattr implementation
  linux-user: call cpu_copy under clone_lock
  target/xtensa: linux-user: rewind pc for restarted syscall
  target/xtensa: fix flush_window_regs

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