[Bug middle-end/69976] Zero the local stack on function exit

[daniel.gutson at tallertechnologies dot com]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=69976

--- Comment #3 from Daniel Gutson <daniel.gutson at tallertechnologies dot com> ---
Those are very good ideas but fell into the land of the backend. The red zone
IIUC is a x86_64 only ABI concept.
What do you think about adding also a -m counterpart option with the same
semantic but for the backend?
Our plan is to address separately the middle end part and the backend part
(initially for x86_64) and subdivide the latter in clobbered registers and red
zone cleaning, so 3 sets of patches.