[Bug c/106571] Implement -Wsection diag

[bp at alien8 dot de via Gcc-bugs]

https://gcc.gnu.org/bugzilla/show_bug.cgi?id=106571

--- Comment #5 from Boris <bp at alien8 dot de> ---
(In reply to Michael Matz from comment #4)
> Boris: what does DECLARE_PER_CPU() expand into?  Are there other attributes
> that could be usefully checked for mismatch between decl and def?

Unfortunately,

DECLARE_PER_CPU(u64, x86_spec_ctrl_current);

expands only to:

extern __attribute__((section(".data..percpu" ""))) __typeof__(u64)
x86_spec_ctrl_current;