[clang] [clang] Check constexpr int->enum conversions consistently. (PR #143034)

[James Y Knight via cfe-commits]

jyknight wrote:

This same code in Boost was already implicated by the 2022 changes, and I reported a bug for it back then. It was fixed a couple years later in Boost 1.86. https://github.com/boostorg/mpl/issues/69#issuecomment-2301411819 mentions two commits that can be backported to older versions of Boost.

https://github.com/llvm/llvm-project/pull/143034