[clang] [clang] Format "array is too large" diagnostics with separators (PR #160260)

[via cfe-commits]

Sirraide wrote:

> It is unfortunately harder than it sounds since we never copy the AP(S)Int into the diagnostic right now :(

I see, yeah. In that case just doing that for diagnostics that are likely to print large numbers is still nice.

https://github.com/llvm/llvm-project/pull/160260