[GNATS 21669] Spurious diagnostic for noexcept in initializer lists

[jhsedg]

Customer bug ID

(boost) identity.cpp, (gnats) 21669 is the reduced test below, 21669a is the full expanded test

Description

​This reduced Boost test generates an unexpected diagnostic:
​
​namespace std {
​template class initializer_list {
​ int *a;
​ unsigned long b;
​ initializer_list(int *, long);
​};
​} // namespace std
​struct {
​ template void operator()(std::initializer_list) noexcept;
​} d;
​struct e {
​ void operator()() const;
​};
​void e::operator()() const {
​ static_assert(noexcept(d({3})), "Noexcept identity");
​}
​[ellen@lin1 debug]$ $CPFE --c++17 --gnu_version 80100 -w /tmp/identiy_ourheaders.reduced.C
​"/tmp/identiy_ourheaders.reduced.C", line 15: error: static assertion failed
​ with "Noexcept identity"
​ static_assert(noexcept(d({3})), "Noexcept identity");
​ ^
​
​1 error detected in the compilation of "/tmp/identiy_ourheaders.reduced.C".
​[ellen@lin1 debug]$