Crash during exception unwinding

https://webkit.org/b/119860

Reviewed by Filip Pizlo.

Add an "Unreachable" NodeType, and then rearrange op_throw and op_throw_reference_error
to plant Throw or ThrowReferenceError followed by a flush and then the Unreachable node.

We need this so that Throw and ThrowReferenceError no longer need to be treated as
terminals and the subsequent flush keeps the activation (and other registers) live.

* dfg/DFGAbstractInterpreterInlines.h:
(JSC::DFG::::executeEffects):
* dfg/DFGByteCodeParser.cpp:
(JSC::DFG::ByteCodeParser::parseBlock):
* dfg/DFGClobberize.h:
(JSC::DFG::clobberize):
* dfg/DFGFixupPhase.cpp:
(JSC::DFG::FixupPhase::fixupNode):
* dfg/DFGNode.h:
(JSC::DFG::Node::isTerminal):
* dfg/DFGNodeType.h:
* dfg/DFGPredictionPropagationPhase.cpp:
(JSC::DFG::PredictionPropagationPhase::propagate):
* dfg/DFGSafeToExecute.h:
(JSC::DFG::safeToExecute):
* dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::compile):

Change-Id: Idb894e780cd3ebe15515d1796c58a339ae54d55f
git-svn-id: http://svn.webkit.org/repository/webkit/trunk@154290 268f45cc-cd09-0410-ab3c-d52691b4dbfc
Reviewed-by: Jocelyn Turcotte <jocelyn.turcotte@digia.com>