JIT: `GetFfr` hw intrinsics are not modelled appropriately by value numbering

[jakobbotsch]

These are nullary HW intrinsics that read from state that we do not model. VN should be giving them new unique VNs to model this. Right now I would expect two GetFfr calls to be CSE'd regardless of interfering intrinsics that may redefine ffr.

cc @dotnet/jit-contrib @dotnet/arm64-contrib

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[jakobbotsch]

Simplest fix is probably just to add it next to the existing case:

runtime/src/coreclr/jit/valuenum.cpp

Lines 13059 to 13068 in 6931b3b

	// Some intrinsics should always be unique
	bool makeUnique = false;
	if (tree->OperIsConvertMaskToVector())
	{
	// We want to ensure that we get a TYP_MASK local to
	// ensure the relevant optimizations can kick in
	makeUnique = true;
	}

[jakobbotsch]

Although, it seems cleaner to give it HW_Flag_SpecialSideEffect_Other and then teach VN that it should always give HW intrinsics with that flag unique VNs. Let me try opening a PR with that change.