Main executables were bypassing the locate module callback that shared
libraries use, preventing custom symbol file location logic from working
consistently.
This PR fix this by
* Adding target context to ModuleSpec
* Leveraging that context to use target search path and platform's
locate module callback in ModuleList::GetSharedModule
This ensures both main executables and shared libraries get the same
callback treatment for symbol file resolution.
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Co-authored-by: George Hu <hyubo@meta.com>
Co-authored-by: George Hu <georgehuyubo@gmail.com>
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