Consolidate the way WTF_USE_PTHREADS is enabled
https://bugs.webkit.org/show_bug.cgi?id=108191

Patch by Laszlo Gombos <l.gombos@samsung.com> on 2013-02-10
Reviewed by Benjamin Poulain.

.:

Remove duplicated definition of WTF_USE_PTHREADS.

WTF_USE_PTHREADS is defined to 1 on all OS(UNIX) environments in
Platform.h.

* Source/cmake/OptionsBlackBerry.cmake:
* Source/cmake/OptionsEfl.cmake:

Source/WTF:

Define WTF_USE_PTHREADS to 1 on all OS(UNIX) environments.

* WTF.gyp/WTF.gyp: Remove duplicated definition of WTF_USE_PTHREADS.
* wtf/Platform.h:

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@142417 268f45cc-cd09-0410-ab3c-d52691b4dbfc