Merge remote-tracking branch 'riku/linux-user-for-upstream' into staging

Merge remote-tracking branch 'riku/linux-user-for-upstream' into staging

# By Peter Maydell (5) and others
# Via Riku Voipio
* riku/linux-user-for-upstream:
  linux-user/syscall.c: Don't warn about unimplemented get_robust_list
  linux-user: Implement accept4
  linux-user: Implement sendfile and sendfile64
  linux-user: make bogus negative iovec lengths fail EINVAL
  linux-user: Fix layout of usage table to account for option text
  linux-user: Add more sparc syscall numbers
  linux-user: Support setgroups syscall with no groups
  linux-user: fix futex strace of FUTEX_CLOCK_REALTIME
  linux-user/syscall.c: handle FUTEX_WAIT_BITSET in do_futex
  linux-user: improve print_fcntl()
  linux-user: Add Alpha socket constants