[clang] [Driver][BoundsSafety] Add -fbounds-safety-experimental flag (PR #70480)

[Dan Liew via cfe-commits]

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@@ -330,6 +330,9 @@ def warn_alias_with_section : Warning<
   "as the %select{aliasee|resolver}2">,
   InGroup<IgnoredAttributes>;
 
+def error_bounds_safety_lang_not_supported : Error<
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delcypher wrote:

Nit: A lot of the error diagnostics use `err` as a preifx rather than `error`.

https://github.com/llvm/llvm-project/pull/70480