[Mac] WTFThreadData should use _pthread_getspecific_direct().
<https://webkit.org/b/130320>

Hack WTFThreadData to use a direct key for TLS access when available.
This mechanism uses a dedicated segment register and is the same way
we implement the fast path in FastMalloc.

Reviewed by Darin Adler.

* wtf/FastMalloc.cpp:
* wtf/WTFThreadData.cpp:
(WTF::WTFThreadData::createAndRegisterForGetspecificDirect):
* wtf/WTFThreadData.h:
(WTF::wtfThreadData):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@165725 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Buildfix after r165725 for non Mac platforms.

Patch by Tamas Gergely <tgergely.u-szeged@partner.samsung.com> on 2014-03-17
Reviewed by Csaba Osztrogonác.

* wtf/WTFThreadData.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@165726 268f45cc-cd09-0410-ab3c-d52691b4dbfc
One more fix after r165725.

Patch by Tamas Gergely <tgergely.u-szeged@partner.samsung.com> on 2014-03-17
Reviewed by Csaba Osztrogonác.

* wtf/WTFThreadData.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@165729 268f45cc-cd09-0410-ab3c-d52691b4dbfc