[Bug c/106571] Implement -Wsection diag

[bp at alien8 dot de]

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

--- Comment #2 from Boris <bp at alien8 dot de> ---
How can you check a mismatch if only the definition has the section attribute?

Here's the kernel commit which fixes this for clang:

https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=db886979683a8360ced9b24ab1125ad0c4d2cf76

there's the same example in the commit message.