Reviewed by Oliver Hunt.

        Provide a class type for a generated block of JIT code.
        Also changes the return address -> bytecode index map to
        track the return addess as an unsigned offset into the code
        instead of a ptrdiff_t in terms of void**s - the latter is
        equal to the actual offset / sizeof(void*), making it a
        potentially lossy representation.

        * JavaScriptCore.xcodeproj/project.pbxproj:
        * assembler/AbstractMacroAssembler.h:
        (JSC::AbstractMacroAssembler::PatchBuffer::returnAddressOffset):
        * assembler/X86Assembler.h:
        (JSC::X86Assembler::getCallReturnOffset):
        * bytecode/CodeBlock.h:
        (JSC::CallReturnOffsetToBytecodeIndex::CallReturnOffsetToBytecodeIndex):
        (JSC::getCallReturnOffset):
        (JSC::CodeBlock::getBytecodeIndex):
        (JSC::CodeBlock::jitCode):
        (JSC::CodeBlock::callReturnIndexVector):
        * interpreter/Interpreter.cpp:
        (JSC::Interpreter::execute):
        (JSC::Interpreter::cti_vm_dontLazyLinkCall):
        (JSC::Interpreter::cti_vm_lazyLinkCall):
        * jit/JIT.cpp:
        (JSC::JIT::privateCompile):
        * jit/JIT.h:
        (JSC::):
        * jit/JITCall.cpp:
        (JSC::JIT::linkCall):
        * jit/JITCode.h: Added.
        (JSC::):
        (JSC::JITCode::JITCode):
        (JSC::JITCode::operator bool):
        (JSC::JITCode::addressForCall):
        (JSC::JITCode::offsetOf):
        (JSC::JITCode::execute):



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@40813 268f45cc-cd09-0410-ab3c-d52691b4dbfc