[Bug c/71255] Implement #pragma may_alias

[mpolacek at gcc dot gnu.org]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=71255

--- Comment #27 from Marek Polacek <mpolacek at gcc dot gnu.org> ---
Typo: I meant __GNUC__ >= 7 as this is fixed for GCC 7 and onwards.