linux-user: Fix getresuid, getresgid if !USE_UID16

linux-user: Fix getresuid, getresgid if !USE_UID16

The size of the UID/GID types depends on whether USE_UID16 is
defined. Define a new put_user_id() which writes a uid/gid
type to guest memory. This fixes getresuid and getresgid, which
were always storing 16 bits even if the uid type was 32 bits.

Reported-by: Michael Matz <[email protected]>
Signed-off-by: Peter Maydell <[email protected]>
Signed-off-by: Riku Voipio <[email protected]>
Reviewed-by: Andreas Färber <[email protected]>
Reviewed-by: Richard Henderson <[email protected]>