various: add rustc_lint_diagnostics to diag fns

The `rustc_lint_diagnostics` attribute is used by the diagnostic
translation/struct migration lints to identify calls where
non-translatable diagnostics or diagnostics outwith impls are being
created. Any function used in creating a diagnostic should be annotated
with this attribute so this commit adds the attribute to many more
functions.

Signed-off-by: David Wood <david.wood@huawei.com>

compiler/rustc_expand/src/lib.rs

@@ -9,6 +9,7 @@
 #![feature(proc_macro_diagnostic)]
 #![feature(proc_macro_internals)]
 #![feature(proc_macro_span)]
+#![feature(rustc_attrs)]
 #![feature(try_blocks)]
 #![recursion_limit = "256"]