[clang] [clang][llvm-lit] Rewrite constexpr vectors test to use element access (PR #102757)

[Amr Hesham via cfe-commits]

AmrDeveloper wrote:

> > Should we merge now?
> 
> Well, there seem to be some CI failures, so unless those are unrelated, they’ll have to be resolved first.

It was related to a file that not removed on the linux server

`rm: cannot remove Output.TestFile: Permission deniedz

https://github.com/llvm/llvm-project/pull/102757