[clang-tools-extra] [clang-tidy] Rename 'cert-dcl50-cpp' to 'modernize-avoid-variadic-functions' (PR #157737)

[Baranov Victor via cfe-commits]

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@@ -0,0 +1,17 @@
+.. title:: clang-tidy - modernize-avoid-variadic-functions
+
+modernize-avoid-variadic-functions
+==================================
+
+Find all function definitions (but not declarations) of C-style variadic
+functions.
+
+Instead of C-style variadic functions, C++ function parameter pack or currying
+should be used.
+
+References
+----------
+
+This check corresponds to the CERT C++ Coding Standard rule
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vbvictor wrote:

I'd place link to CERT in both docs (hoping it won't become outdated)

https://github.com/llvm/llvm-project/pull/157737