Fix testkjs in 64-bit.

Fix testkjs in 64-bit.

When built for 64-bit the TCMalloc spin lock uses pthread mutexes rather than a custom spin lock
implemented in assembly.  If we fail to initialize the pthread mutex, attempts to lock or unlock
it will fail and trigger a call to abort.

Reviewed by Darin.

* wtf/FastMalloc.cpp: Initialize the spin lock so that we can later lock and unlock it.
* wtf/TCSpinLock.h: Add an Init method to the optimised spin lock.

git-svn-id: https://svn.webkit.org/repository/webkit/trunk@28449 268f45cc-cd09-0410-ab3c-d52691b4dbfc