[clang] [Clang] improve -Wstring-concatenation to warn on every missing comma in initializer lists (PR #154018)

[Oleksandr T. via cfe-commits]

a-tarasyuk wrote:

@ilovepi @nathanchance @AaronBallman I’ve opened a PR to roll back the changes for now, to finalize the intended behavior of this flag.

https://github.com/llvm/llvm-project/pull/154018