[llvm] undo breaking changes from "Reduce AsmPrinterHandlers virt. fn calls" without reverting the performance gains (PR #122297)

[Jameson Nash via llvm-commits]

vtjnash wrote:

Okay, looks like that was a latent bug from #96785 having forgotten to duplicate a line of code for endFunction, which triggered here due to being only a partial revert instead of a full revert. This rework is why I wanted to NAK the original PR, when it was not shown to be an actual measurable improvement, just API breakage. But anyways, this should be good to go now, with the requested improvements to this PR and still keeping the minor reduction in no-op function call counts. Thanks for reviewing.

https://github.com/llvm/llvm-project/pull/122297