[Bug c/107951] Invalid flexible array use not detected in nested structs by the C frontend

[pinskia at gcc dot gnu.org via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=107951

--- Comment #3 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
r0-44662-g2984fe64968ad7 added that documentation.
PR 15749 shows that at one point there was code floating around (glibc?) that
uses the extension (_G_iconv_t).