[llvm] [SDPatternMatch] Only match ISD::SIGN_EXTEND in m_SExt (PR #95415)

[via llvm-commits]

c8ef wrote:

> Cleanup the PR title and summary. Title should be something like "[SDPatternMatch] Only match ISD::SIGN_EXTEND in m_SExt" and then refer to #90762 in the summary and explain why we need this.

Fixed. I will be more careful with the PR description and title in the future.

https://github.com/llvm/llvm-project/pull/95415