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

[Vitaly Buka via cfe-commits]

================
@@ -444,6 +444,19 @@ class LangOptionsBase {
     IncompleteOnly = 3,
   };
 
+  enum class ArrayBoundsStrictFlexArraysLevelKind {
----------------
vitalybuka wrote:

To match numerical values, less mental efforts for readers.

```
  enum class ArrayBoundsStrictFlexArraysLevelKind {
    // Use same StrictFlexArrayLevel as compiler.
    None = -1,
    /// Any trailing array member is a FAM.
    Default = 0,
    /// Any trailing array member of undefined, 0, or 1 size is a FAM.
    OneZeroOrIncomplete = 1,
    /// Any trailing array member of undefined or 0 size is a FAM.
    ZeroOrIncomplete = 2,
    /// Any trailing array member of undefined size is a FAM.
    IncompleteOnly = 3,
  };
```

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