[MERGE #2088 @ianwjhalliday] xplat: don't use private heap
[MERGE #2088 @ianwjhalliday] xplat: don't use private heap

Merge pull request #2088 from ianwjhalliday:release/2.0-pre

Do not use private heap on xplat.

Currently with our static linking in node-chakracore our overridden new/delete operators are picked up by node itself.  Use of the private heap leads to instability on shutdown due to the chance that HeapAllocator::Instance is disposed before other allocations.  Using alloc and free instead circumvents this problem.

Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,Microsoft/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore,mrkmarron/ChakraCore