[libcxx-commits] [libcxx] [libc++][hardening] Check that `_LIBCPP_HARDENING_MODE_DEFAULT` is defined (PR #80353)

[Konstantin Varlamov via libcxx-commits]

================
@@ -325,6 +325,11 @@
 // clang-format on
 
 #  ifndef _LIBCPP_HARDENING_MODE
+
+#    ifndef _LIBCPP_HARDENING_MODE_DEFAULT
+#      error _LIBCPP_HARDENING_MODE_DEFAULT is not defined.
----------------
var-const wrote:

Do we want to speculate in the comment as to why that might be the case? E.g.
```cpp
// Normally this macro comes from the `__config_site` header which is generated via CMake.
// If you use a custom build system, please make sure to define `_LIBCPP_HARDENING_MODE_DEFAULT`
// to one of the valid hardening modes.
```

https://github.com/llvm/llvm-project/pull/80353