[clang] [sanitizer] [clang] Introduce fsanitize-bounds-strict-flex-arrays (PR #126163)

[Vitaly Buka via cfe-commits]

vitalybuka wrote:

Usually our tweak flags looks like -fsanitize-<sanitizer>-<option>

"bounds" is a group for (array-bounds + local-bounds)
"undefined" is also group, but we already have -fsanitize-undefined-<options>, but they kind of affect a few sanitizers

so:
`-fsanitize-undefined-strict-flex-arrays`
or 
`-fsanitize-array-bounds-strict-flex-arrays`
?

https://github.com/llvm/llvm-project/pull/126163