[C++ PATCH] diagnose address and decltype of unsatisfied function

[Jason Merrill]

While looking at one of the issues under discussion at the meeting, I 
noticed we weren't diagnosing a couple of cases of unsatisfied 
un-overloaded functions.

It also seems to me that -fconcepts-ts ought to imply -fconcepts for 
pre-C++20 modes.

Tested x86_64-pc-linux-gnu, applying to trunk.
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