[llvm] [FuncSpec] Handle ssa_copy intrinsic calls in InstCostVisitor (PR #114247)

[Hari Limaye via llvm-commits]

hazzlim wrote:

> Great thanks! Unit/regression test?

Added a regression test, as a prior commit so it's more obvious how this change affects things :)

As additional context for this change, this improves the estimation of the CodeSize bonus for a specialization of the function `digits_2` from the SPEC2k17 benchmark `exchange2`, increasing this from 43% to 68% (with `-mcpu=neoverse-{n1|v2}`).

https://github.com/llvm/llvm-project/pull/114247