[clang] [Clang] Tolerate constant evaluation failure when transforming SubstNonTypeTemplateParmExpr in unevaluated contexts (PR #196791)

[via cfe-commits]

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@@ -543,6 +543,7 @@ Bug Fixes in This Version
 - Fixed a crash when parsing invalid ``static_assert`` declarations with string-literal messages (#GH187690).
 - Fixed a potential stack-use-after-return issue in Clang when copy-initializing
   an array via an element-at-a-time copy loop (#GH192026)
+- Fixed a regression where calling a function that takes a class-type parameter by value inside ``decltype`` of a concept could be incorrectly rejected when used as a non-type template argument. (#GH175831)
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wx257osn2 wrote:

[The previous (and my first) PR](https://github.com/llvm/llvm-project/pull/184406) wasn't backported, so I'm not familiar with the process. Would you mind walking me through the steps?

https://github.com/llvm/llvm-project/pull/196791