[Bug c/120850] provide an special __builtin_memset_explicit

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

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=120850

--- Comment #2 from Andrew Pinski <pinskia at gcc dot gnu.org> ---
Using an inline-asm to cause compiler barriers should be enough to stop gcc
from optimizing the code away.