[clang] [clang][Interp] Only emit function_param_value_unknown in C++11 (PR #67990)

[Aaron Ballman via cfe-commits]

AaronBallman wrote:

> https://reviews.llvm.org/D156565 hasn't been merged as far as I can tell and it's the only test case I have for this. :(

Ah shoot, let me ping that review and see if I can get it accepted and landed so we can have test coverage.

https://github.com/llvm/llvm-project/pull/67990