swift234

Heap: avoid reentrancy when Instruments enables ObjectAlloc

We need a custom but simple map table for two reasons:
1) To precisely control our allocations to avoid reentrancy via Instruments.
2) To prepare for out-of-process introspection via Mach VM calls.

This fixes: <rdar://problem/16718231> Swift allocator must not call malloc nor global operator new

Swift SVN r17769