Diagnose declarations that don't declare anything, and fix PR3020.
Examples:
int;
typedef int;

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@61454 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/test/Sema/decl-invalid.c b/test/Sema/decl-invalid.c
index 767d6e6..78a9ee1 100644
--- a/test/Sema/decl-invalid.c
+++ b/test/Sema/decl-invalid.c
@@ -1,6 +1,7 @@
 // RUN: clang %s -fsyntax-only -verify
 
-typedef union <anonymous> __mbstate_t;  // expected-error {{declaration of anonymous union must be a definition}}
+// See Sema::ParsedFreeStandingDeclSpec about the double diagnostic
+typedef union <anonymous> __mbstate_t;  // expected-error {{declaration of anonymous union must be a definition}} expected-error {{declaration does not declare anything}}
 
 
 // PR2017
@@ -9,3 +10,9 @@
   int r[x()];  // expected-error {{size of array has non-integer type 'void'}}
 }
 
+int; // expected-error {{declaration does not declare anything}}
+typedef int; // expected-error {{declaration does not declare anything}}
+const int; // expected-error {{declaration does not declare anything}}
+struct; // expected-error {{declaration of anonymous struct must be a definition}} // expected-error {{declaration does not declare anything}}
+typedef int I;
+I; // expected-error {{declaration does not declare anything}}