Improved collapse_debuginfo attribute, added command-line flag (no|external|yes)

compiler/rustc_expand/src/errors.rs

@@ -58,6 +58,13 @@ pub(crate) struct ResolveRelativePath {
     pub path: String,
 }
 
+#[derive(Diagnostic)]
+#[diag(expand_collapse_debuginfo_illegal)]
+pub(crate) struct CollapseMacroDebuginfoIllegal {
+    #[primary_span]
+    pub span: Span,
+}
+
 #[derive(Diagnostic)]
 #[diag(expand_macro_const_stability)]
 pub(crate) struct MacroConstStability {