[DynInst_API:] commit: fix template instantiation in emitElf

[Bill Williams <bill@xxxxxxxxxxx>]

As per subject. My language lawyering was not up to snuff.

The following pattern of explicit instantiation appears to have the 
broadest support:
foo.h:
template<typename T> class foo
{
    // declaration
};
extern template class foo<bar>;
extern template class foo<baz>;

foo.C:

template<typename T> foo<T>::func()
{
}
...

template class foo<bar>;
template class foo<baz>;

Open to suggestions for still-more-portable ways to make explicit 
instantiations properly visible without having giant implementations 
living in header files.
--bw