[BOLT] Fix iterator bugs (#190978) Fix iterator misuse in four BOLT passes, caught by _GLIBCXX_DEBUG (enabled via LLVM_ENABLE_EXPENSIVE_CHECKS=ON). * AllocCombiner: combineAdjustments() erases instructions while iterating in reverse via llvm::reverse(BB), invalidating the reverse iterator. Defer erasures to after the loop using a SmallVector. * ShrinkWrapping: processDeletions() uses std::prev(BB.eraseInstruction(II)) which is undefined when II == begin(). Restructure to standard forward iteration with erase. * DataflowAnalysis: run() unconditionally dereferences BB->rbegin(), which crashes on empty basic blocks (possible after the ShrinkWrapping fix). Guard with an emptiness check. * IndirectCallPromotion: rewriteCall() dereferences the end iterator via &(*IndCallBlock.end()). Replace with &IndCallBlock.back(). * TailDuplication: constantAndCopyPropagate() uses std::prev(OriginalBB.eraseInstruction(Itr)) which is undefined when Itr == begin(). Restructure to standard forward iteration with erase.
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