[Bug c/69982] missing warning when using __thread with -std=c99 -pedantic

[vincent-gcc at vinc17 dot net]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69982

--- Comment #5 from Vincent Lefèvre <vincent-gcc at vinc17 dot net> ---
(In reply to Marek Polacek from comment #4)
> Doesn't seem like a bug.

Could you argument? Why is __thread regarded as an extension but _Thread_local
cannot be regarded as an extension as well? And is there any reason to disable
the warning for such an extension?