[llvm] [DebugInfo][Reassociate] Fix missing debug location drop (PR #95355)

[Orlando Cazalet-Hyams via llvm-commits]

================
@@ -0,0 +1,51 @@
+; RUN: opt < %s -passes=reassociate -S | FileCheck %s
+
----------------
OCHyams wrote:

Please can you add a brief comment to the test explaining its purpose?

https://github.com/llvm/llvm-project/pull/95355