constexpr and main

Clause / Subclause / Annex: 
3.6.1
Para/Table/Figure: 
3
Comment type: 
Te
Comment / justification for change: 

Do we really want to allow: constexpr int main() { return 0; }
as a valid program?

Recommended change: 

Add constexpr to the list of ill-formed things to annotate main

MB: 
UK