android: backport pty implementation from aosp/master

and use compatible hasmntopt() return type

To fix all swapon/off compilation warnings

Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>

Change-Id: I4ee6e7752eab84de4566ae86a90171b8241fcaea
Fix remaining bionic warnings

smemcap: uid_t is unsigned

Change-Id: I170b16f2e091b99f971fb518bf0106c0e92adfdd
Fix other warnings no more shown in 1.23

Change-Id: Ie402a35cc68b63e4e6ff45e91de48b2670d1ffa9