[clang] Suppress printing lambda body for constexpr diagnostics (PR #185800)

[Corentin Jabot via cfe-commits]

cor3ntin wrote:

> I have squashed the commits into a single commit via fixups. I think this is ready for submission. PTAL.

For future reference, this is actually undesirable as it messes up with Github. Once a PR lands, we merge with squash 
(and the pr description becomes the commit message)

https://github.com/llvm/llvm-project/pull/185800