[llvm] [NFCI][Globals]For GlobalObjects, add updateSectionPrefix and change setSectionPrefix to handle empty strings (PR #158460)

[Mingming Liu via llvm-commits]

https://github.com/mingmingl-llvm commented:

> The title and summary are both mechanical. Maybe add a 1 sentence description of why this change is needed?

Sure! The updated PR description points to the use case. 

Also clicked 'ready for review' to make this non-draft. Forgot to do this when I requested reviews before.

https://github.com/llvm/llvm-project/pull/158460