x86: Deprecate a.out support

x86: Deprecate a.out support

Linux supports ELF binaries for ~25 years now.  a.out coredumping has
bitrotten quite significantly and would need some fixing to get it into
shape again but considering how even the toolchains cannot create a.out
executables in its default configuration, let's deprecate a.out support
and remove it a couple of releases later, instead.

Signed-off-by: Borislav Petkov <[email protected]>
Acked-by: Richard Weinberger <[email protected]>
Cc: Al Viro <[email protected]>
Cc: Anton Ivanov <[email protected]>
Cc: Jann Horn <[email protected]>
Cc: <[email protected]>
Cc: <[email protected]>
Cc: lkml <[email protected]>
Cc: Matthew Wilcox <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>