android: backport pty implementation from aosp/master

This is not (yet) in l-preview branch but on master
The only way to prevent duplicated includes was to
test the existence of a new constant added after
l-preview bionic source release.

Also use compatible hasmntopt() return type
(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
Android.mk: toggle l-preview config flag

Change-Id: I4465b88a0337f5f267d501a94b2f71f8ef07b318
android: fix building errors with Android L

Tested OK with Android L PDK LRW17D.

The asm files are regenerated by Android L gensyscalls.py.
syscalls: restore compatibilty with current branch

on arm __NR_stime constant is undefined in asm/unistd.h

add also BIONIC_L define for assembly files (syscalls)
tested on arm and x86 (not on mips)

Change-Id: If5b6a6d3f8b4c10339f8e7b0bf340d02c1cf26cb
Signed-off-by: Tanguy Pruvot <tanguy.pruvot@gmail.com>