This series switches compat wait4() and waitid() variants away from set_fs() use. A couple of helpers (kernel_wait4() and kernel_waitid()) are introduced, copying siginfo/rusage to userland is taken to sys_wait...(). That allows both to simplify the guts of do_wait() machinery and avoid messing with set_fs() in compat variants of these syscalls.
Lightly tested, seems to survive without regressions. Please,
review.
