[GVNSink] Make GVNSink resistant against self referencing instructions (PR36954)

Before this change GVNSink pass suffers from stack overflow while processing self referenced instruction in unreachable basic block.
According [1] and [2] it's reasonable to make pass resistant against self referencing instructions.
To fix issue we skip sinking analysis when we reach instruction coming from unreachable block.

[1] https://groups.google.com/g/llvm-dev/c/843Tig9IzwA
[2] https://lists.llvm.org/pipermail/llvm-dev/2015-February/082629.html

Differential Revision: https://reviews.llvm.org/D113897