[Bug c++/50871] [C++0x] G++ fails to reject explicitly-defaulted function definition with different exception spec in system headers

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=50871

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-10-27 13:31:17 UTC ---
It would work for my original case, yes.  There are other cases where the
warning is not a pedwarn, but is just suppressed by system_header while
building the lib.

But it occurred to me that we currently rely on system_header to suppress
warnings about using variadic templates in c++98 mode