https://bugs.webkit.org/show_bug.cgi?id=115468

Reviewed by Geoffrey Garen.

This makes the main thread modify the transition table while holding a lock. Note
that the GC might modify its weak pointers without locking, but the GC will lock out
the compilation thread anyway. The map will then only reshape in response to add()
and set(), which happen while holding a lock.

This allows the compilation thread to now query transition tables safely, provided it
holds a lock when doing so.

Also changed LLVM asm printer initialization to just initialize the X86 one. It makes
sense for us to just initialize the asm printer(s) that we actually use; you could
imagine us being linked to a system LLVM that has cross-compilation support; there is
no point in the WebKit or JSC process doing work to initialize all of those targets.
That part was rubber stamped by Mark Hahnenberg.

* bytecode/PutByIdStatus.cpp:
(JSC::PutByIdStatus::computeFor):
* runtime/InitializeThreading.cpp:
(JSC::initializeThreadingOnce):
* runtime/Structure.cpp:
(JSC::Structure::addPropertyTransitionToExistingStructureImpl):
(JSC::Structure::addPropertyTransitionToExistingStructure):
(JSC):
(JSC::Structure::addPropertyTransitionToExistingStructureConcurrently):
(JSC::Structure::addPropertyTransition):
(JSC::Structure::nonPropertyTransition):
* runtime/Structure.h:
(Structure):

git-svn-id: http://svn.webkit.org/repository/webkit/trunk@153140 268f45cc-cd09-0410-ab3c-d52691b4dbfc