[llvm] [SDAG] Limit sincos/frexp stack slot folding to stores chained to entry (PR #115906)

[Benjamin Maxwell via llvm-commits]

MacDue wrote:

> Please check the buildbot failure; LGTM if it's not related.

Thanks :+1:  The failing test is `lldb-api :: source-manager/TestSourceManager.py`, so I think this is fine. 

https://github.com/llvm/llvm-project/pull/115906