[clang] Introduce paged vector (PR #66430)

[Vassil Vassilev via cfe-commits]

vgvassilev wrote:

> @vgvassilev I've seen other tests use the pattern from my fix. Feel free to overwrite with your version if that's preferred.

Too late in the night in my end and I closed my laptop already. I am fine with your fix - I find the use of the macro I proposed cleaner though. 

https://github.com/llvm/llvm-project/pull/66430