[llvm] [SLP][REVEC] Fix insertelement has multiple uses. (PR #102329)

[Han-Kuan Chen via llvm-commits]

HanKuanChen wrote:

> Is this fixing a miscompilation or is this an enhancement?

This is a bug fix **only** when REVEC is enabled.

https://github.com/llvm/llvm-project/pull/102329