[Bug c++/90320] [7/8/9/10 Regression] Explicit constructor called implicitly

[redi at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=90320

--- Comment #2 from Jonathan Wakely <redi at gcc dot gnu.org> ---
(In reply to Adam Mitz from comment #0)
> May be related to https://gcc.gnu.org/bugzilla/show_bug.cgi?id=87605 but
> this doesn't involve the ternary operator.

It's similar, but I don't think it's the same bug, because the example in PR
87605 was always incorrectly accepted by GCC. The one here used to be rejected
and so is a regression.