[clang] [clang][ssaf] Add UnsafeBufferUsage summary data structures (PR #181067)

[Balázs Benics via cfe-commits]

https://github.com/steakhal commented:

Ah :O , I've just realised that I forgot to send my review comments.
Sorry about this delay.

https://github.com/llvm/llvm-project/pull/181067