add more test cases

Author: a-tarasyuk

clang/lib/Parse/Parser.cpp

@@ -1050,6 +1050,7 @@ Parser::ParseExternalDeclaration(ParsedAttributes &Attrs,
   case tok::kw_extern:
     if (getLangOpts().CPlusPlus && NextToken().is(tok::kw_template)) {
       ProhibitAttributes(Attrs);
+      ProhibitAttributes(DeclSpecAttrs);
       // Extern templates
       SourceLocation ExternLoc = ConsumeToken();
       SourceLocation TemplateLoc = ConsumeToken();

clang/test/Parser/extern-template-attributes.cpp

@@ -1,6 +1,8 @@
-// RUN: %clang_cc1 -std=c++17 -verify %s
+// RUN: %clang_cc1 -std=c++17 -fms-extensions -verify %s
 
 template <class>
 struct S {};
 
-[[deprecated]] extern template struct S<int>; // expected-error {{an attribute list cannot appear here}}
+[[deprecated]] extern template struct S<int>;              // expected-error {{an attribute list cannot appear here}}
+__attribute__((deprecated)) extern template struct S<int>; // expected-error {{an attribute list cannot appear here}}
+__declspec(deprecated) extern template struct S<int>;      // expected-error {{expected unqualified-id}}