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

[Younan Zhang via cfe-commits]

https://github.com/zyn0217 commented:

Thanks, while I'm not opposed to adding some workarounds to get the behavior back, I think I need @mizvekov's thought on this (He fixed this function)

Strictly speaking one shouldn't expect that they are able to instantiate anything from an unevaluated context, however given that we're still lack of the instantiation-on-demand machineary #173537 I think tolerating the behavior is ... harmless?

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