[clang] Add option -fstdlib-hardening= (PR #78763)

[Louis Dionne via cfe-commits]

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@@ -275,6 +275,8 @@ def warn_drv_unknown_argument_clang_cl_with_suggestion : Warning<
   InGroup<UnknownArgument>;
 def err_drv_unknown_target_triple : Error<"unknown target triple '%0'">;
 
+def err_drv_stdlib_hardening_unavailable : Error<"libc++ hardening is available only when libc++ is used">;
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ldionne wrote:

```suggestion
def err_drv_stdlib_hardening_unavailable : Error<"standard library hardening is available only when libc++ is used">;
```

https://github.com/llvm/llvm-project/pull/78763