Remove link_section and linkage as extern indicators

Author: arcnmx

src/libsyntax/attr.rs

@@ -318,8 +318,6 @@ pub fn find_export_name_attr(diag: &Handler, attrs: &[Attribute]) -> Option<Inte
 
 pub fn contains_extern_indicator(attrs: &[Attribute]) -> bool {
     contains_name(attrs, "no_mangle") ||
-        contains_name(attrs, "link_section") ||
-        contains_name(attrs, "linkage") ||
         contains_name(attrs, "export_name")
 }