This changes the SimplifyLibCalls utility to accept an IRBuilderBase, which allows us to pass through the IRBuilder used by InstCombine. This will ensure that new instructions get added to the worklist. The annotated test-case drops from 4 to 2 InstCombine iterations thanks to this.
To achieve this, I'm adding an IRBuilderBase::OperandBundlesGuard, which is basically the same as the existing InsertPointGuard and FastMathFlagsGuard, but for operand bundles. Also add a setDefaultOperandBundles() method so these can be set outside the constructor.