Reviewed by Sam "WX" Weinig.

        Allow the JIT to operate without relying on use of RWX memory, on platforms where this is supported.

        This patch adds a switch to Platform.h (ENABLE_ASSEMBLER_WX_EXCLUSIVE) which enables this mode of operation.
        When this flag is set, all executable memory will be allocated RX, and switched to RW only whilst being
        modified.  Upon completion of code generation the protection is switched back to RX to allow execution.

        Further optimization will be required before it is desirable to enable this mode of operation by default;
        enabling this presently incurs a 5%-10% regression.

        (Submitting disabled - no performance impact).

        * assembler/AbstractMacroAssembler.h:
        (JSC::AbstractMacroAssembler::CodeLocationInstruction::repatchLoadToLEA):
        (JSC::AbstractMacroAssembler::CodeLocationLabel::fromFunctionPointer):
        (JSC::AbstractMacroAssembler::CodeLocationJump::relink):
        (JSC::AbstractMacroAssembler::CodeLocationCall::relink):
        (JSC::AbstractMacroAssembler::CodeLocationNearCall::relink):
        (JSC::AbstractMacroAssembler::CodeLocationDataLabel32::repatch):
        (JSC::AbstractMacroAssembler::CodeLocationDataLabelPtr::repatch):
        (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkCallerToTrampoline):
        (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkCallerToFunction):
        (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkNearCallerToTrampoline):
        (JSC::AbstractMacroAssembler::ProcessorReturnAddress::relinkNearCallerToFunction):
        (JSC::AbstractMacroAssembler::PatchBuffer::PatchBuffer):
        (JSC::AbstractMacroAssembler::PatchBuffer::~PatchBuffer):
        (JSC::AbstractMacroAssembler::PatchBuffer::link):
        (JSC::AbstractMacroAssembler::PatchBuffer::patch):
        (JSC::AbstractMacroAssembler::PatchBuffer::performFinalization):
        (JSC::::CodeLocationCommon::nearCallAtOffset):
        (JSC::::CodeLocationCall::CodeLocationCall):
        (JSC::::CodeLocationNearCall::CodeLocationNearCall):
        * assembler/AssemblerBuffer.h:
        (JSC::AssemblerBuffer::executableCopy):
        * assembler/X86Assembler.h:
        (JSC::CAN_SIGN_EXTEND_U32_64):
        (JSC::X86Assembler::linkJump):
        (JSC::X86Assembler::linkCall):
        (JSC::X86Assembler::patchPointer):
        (JSC::X86Assembler::relinkJump):
        (JSC::X86Assembler::relinkCall):
        (JSC::X86Assembler::repatchInt32):
        (JSC::X86Assembler::repatchPointer):
        (JSC::X86Assembler::repatchLoadToLEA):
        (JSC::X86Assembler::patchInt32):
        (JSC::X86Assembler::patchRel32):
        * jit/ExecutableAllocator.h:
        (JSC::ExecutableAllocator::):
        (JSC::ExecutableAllocator::makeWritable):
        (JSC::ExecutableAllocator::makeExecutable):
        * jit/ExecutableAllocatorFixedVMPool.cpp:
        (JSC::FixedVMPoolAllocator::FixedVMPoolAllocator):
        * jit/ExecutableAllocatorPosix.cpp:
        (JSC::ExecutablePool::systemAlloc):
        (JSC::ExecutablePool::systemRelease):
        (JSC::ExecutableAllocator::reprotectRegion):
        * jit/ExecutableAllocatorWin.cpp:
        * jit/JITPropertyAccess.cpp:
        (JSC::JIT::patchGetByIdSelf):
        (JSC::JIT::patchPutByIdReplace):
        * wtf/Platform.h:



git-svn-id: http://svn.webkit.org/repository/webkit/trunk@44341 268f45cc-cd09-0410-ab3c-d52691b4dbfc