https://gcc.gnu.org/bugzilla/show_bug.cgi?id=78440
--- Comment #1 from Markus Trippelsdorf <trippels at gcc dot gnu.org> --- except.spec/5: »If any declaration of a function has an exception-specification that is not a noexcept-specification allowing all exceptions, all declarations, including the definition and any explicit specialization, of that function shall have a compatible exception-specification. If any declaration of a pointer to function, reference to function, or pointer to member function has an exception-specification, all occurrences of that declaration shall have a compatible exception-specification. If a declaration of a function has an implicit exception specification, other declarations of the function shall not specify an exception-specification. In an explicit instantiation an exception-specification may be specified, but is not required. If an exception-specification is specified in an explicit instantiation directive, it shall be compatible with the exception-specifications of other declarations of that function. A diagnostic is required only if the exception-specifications are not compatible within a single translation unit.«
