The return pointer of bsearch function should have bounds declared

[secure-sw-dev-bot]

This issue was copied from checkedc/checkedc-clang#560

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• The bsearch function is a polymorphic generic function in checked c whose return type is _Ptr where T is defined at callsites
• Currently we cannot provide bounds for the returned pointer. Ideally we would want the return pointer to be, _Array_ptr with bounds (base, (char *)base + (size * nmemb)).

This will make sure that the returned pointer is actually within the bounds of the input array on which the search is made.