[clang] [clang] Note that optnone and target attributes do not apply to nested functions (PR #82815)

[Sam McCall via cfe-commits]

https://github.com/sam-mccall approved this pull request.

Makes sense to me. If this ends up applying to lots of attributes then maybe we should hoist the text somewhere common, but agree that it doesn't seem to.

https://github.com/llvm/llvm-project/pull/82815