Android ucontext refinements (upstream backport).

This is a forward-compatible patch to avoid naming/type conflicts in
the near future, when the Android C library will be updated to provide
mcontext_t/ucontext_t properly.

Note that this changes the naming convention used to access the
register values from mcontext_t, to follow current ARM GLibc (this
is also the convention being adopted by Android).

+ Android provides gettid() (all API levels) so use it instead of
  relying on syscall().

This is a backport of http://code.google.com/p/v8/source/detail?r=12250

See http://code.google.com/p/android/issues/detail?id=34784 for more
context.

Change-Id: Id1fe5489eea8a51d0210858bf91132191f967822
1 file changed