DFG backend Branch handling has duplicate code and dead code
https://bugs.webkit.org/show_bug.cgi?id=110162

Reviewed by Mark Hahnenberg.
        
Streamline the code, and make the 64 backend's optimizations make more sense
(i.e. not be dead code).

* dfg/DFGSpeculativeJIT32_64.cpp:
(JSC::DFG::SpeculativeJIT::compile):
* dfg/DFGSpeculativeJIT64.cpp:
(JSC::DFG::SpeculativeJIT::emitBranch):
(JSC::DFG::SpeculativeJIT::compile):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@143276 268f45cc-cd09-0410-ab3c-d52691b4dbfc