Reviewed by Alexey Proskuryakov.

        https://bugs.webkit.org/show_bug.cgi?id=21571
        VoidPtrPair breaks CTI on Linux

        The VoidPtrPair return change made in r37457 does not work on Linux
        since POD structs aren't passed in registers.

        This patch uses a union to vectorize VoidPtrPair to a uint64_t and
        matches Darwin/MSVC fixing CTI/WREC on Linux.

        Alexey reports no measurable change in Mac performance with this fix.

        * VM/Machine.cpp:
        (JSC::Machine::cti_op_call_JSFunction):
        (JSC::Machine::cti_op_construct_JSConstruct):
        (JSC::Machine::cti_op_resolve_func):
        (JSC::Machine::cti_op_post_inc):
        (JSC::Machine::cti_op_resolve_with_base):
        (JSC::Machine::cti_op_post_dec):
        * VM/Machine.h:
        (JSC::):


git-svn-id: http://svn.webkit.org/repository/webkit/trunk@37995 268f45cc-cd09-0410-ab3c-d52691b4dbfc