Auto merge of rust-lang#117727 - saethlin:inline-derived-fmt, r=<try>

Emit #[inline] on derive(Debug)

Breaking out part of rust-lang#116583 (comment)

r? `@ghost`

Author: bors

compiler/rustc_builtin_macros/src/deriving/debug.rs

@@ -33,7 +33,7 @@ pub fn expand_deriving_debug(
             explicit_self: true,
             nonself_args: vec![(fmtr, sym::f)],
             ret_ty: Path(path_std!(fmt::Result)),
-            attributes: ast::AttrVec::new(),
+            attributes: thin_vec![cx.attr_word(sym::inline, span)],
             fieldless_variants_strategy:
                 FieldlessVariantsStrategy::SpecializeIfAllVariantsFieldless,
             combine_substructure: combine_substructure(Box::new(|a, b, c| {