Add a fixit for attributes incorrectly placed prior to 'struct/class/enum' keyword.

Suggest moving the following erroneous attrib list (based on location)
[[]] struct X;  
to 
struct [[]] X;

Additionally, added a fixme for the current implementation that diagnoses misplaced attributes to consider using the newly introduced diagnostic (that I think is more user-friendly).

llvm-svn: 321449
diff --git a/clang/test/Parser/cxx-decl.cpp b/clang/test/Parser/cxx-decl.cpp
index 58ad0807..1a24520 100644
--- a/clang/test/Parser/cxx-decl.cpp
+++ b/clang/test/Parser/cxx-decl.cpp
@@ -199,7 +199,7 @@
 // expected-error@-2 {{expected expression}}
 // expected-error@-3 {{expected unqualified-id}}
 #else
-// expected-error@-5 {{an attribute list cannot appear here}}
+// expected-error@-5 {{misplaced attributes}}
 #endif
 
 namespace test7 {