Rollup merge of #146766 - nikic:global-alloc-attr, r=nnethercote

Add attributes for #[global_allocator] functions

Emit `#[rustc_allocator]` etc. attributes on the functions generated by the `#[global_allocator]` macro, which will emit LLVM attributes like `"alloc-family"`. If the module with the global allocator participates in LTO, this ensures that the attributes typically emitted on the allocator declarations are not lost if the definition is imported.

There is a similar issue when the allocator shim is used, but I've opted not to fix that case in this PR, because doing that cleanly is somewhat gnarly.

Related to rust-lang/rust#145995.

Author: Zalathar