[clang] [clang][ExprConst] allow single element access of vector object to be constant expression (PR #72607)

[Aaron Ballman via cfe-commits]

https://github.com/AaronBallman commented:

Sorry, this fell off my radar for a while. The only concern I have is with accidentally allowing `&V[0]` to mean something; it would be good to reject that and add a test for that situation. Otherwise, this looks reasonable to me.

https://github.com/llvm/llvm-project/pull/72607