libgomp: Implementing THREADPRIVATE construct

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1 9.6 Implementing THREADPRIVATE construct
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1 In _most_ cases we can map this directly to '__thread'.  Except that OMP
1 allows constructors for C++ objects.  We can either refuse to support
1 this (how often is it used?)  or we can implement something akin to
1 .ctors.
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1    Even more ideally, this ctor feature is handled by extensions to the
1 main pthreads library.  Failing that, we can have a set of entry points
1 to register ctor functions to be called.
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