i#1551 Port DynamoRIO to ARM: rename segment_register to thread_register

i#1551 Port DynamoRIO to ARM: rename segment_register to thread_register
- rename is_segment_register_initialized to is_thread_register_initialized
- rename read_selector to read_thread_register
- implement read_thread_register on ARM

R=bruening@google.com
BUG=1551

Committed: https://code.google.com/p/dynamorio/source/detail?r=3018

[zhaoqin, 2014-11-21 20:36:00]

Please take a look

[bruening, 2014-11-22 15:34:47]

LGTM w/ request

https://codereview.appspot.com/176140043/diff/20001/core/unix/tls.h
File core/unix/tls.h (right):

https://codereview.appspot.com/176140043/diff/20001/core/unix/tls.h#newcode138
core/unix/tls.h:138: asm volatile("mrc  p15, 0, %0, c13, c0, 3" : "=r"(sel));
Ditto

https://codereview.appspot.com/176140043/diff/20001/core/unix/tls.h#newcode144
core/unix/tls.h:144: asm volatile("mrc  p15, 0, %0, c13, c0, 2" : "=r"(sel));
"p15" and "c13" and "c0" and "2" should be named constants -- or at least have a
comment explaining these magic numbers.

[zhaoqin, 2014-11-24 16:30:31]

Committed patchset #2 (id:20001) manually as 3018 (presubmit successful).