[clang] [Clang] Fix missing -Warray-bounds warning on member function calls. (PR #179647)

[Devon Loehr via cfe-commits]

DKLoehr wrote:

It seems like this is causing some new failures in some libraries used by chromium (for example, [simdutf](https://github.com/simdutf/simdutf/blob/97eb03dbfcb40e66a5a4d3a6ca588d9b288ee5fb/src/generic/utf8_to_utf16/utf8_to_utf16.h#L166)). It seems like the fix is probably to use `if constexpr`, but it'll take some time to patch everything.

It's unfortunate that we weren't catching this before, but can we put the new behavior behind a new `-Warray-bounds-member` flag so we can disable it until all the instances are fixed?

https://github.com/llvm/llvm-project/pull/179647