Therefore, the only thing I can hope for is some general Inline debugging/troubleshooting advice. For starters, I would love to know how to find out which function in my code is causing Inline C to generate a reference to XS_unpack_charPtrPtr.

Whether it will help or not ... but you could start by adding:

#define XS_unpack_charPtrPtr ___something___never___defined
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at the top of your code after any #includes. That ought to cause any references to it to bellyache along with line numbers. It might give you a starting point.