Diagnose invalid uses of tagged types with a missing tag. For example, in:

struct xyz { int y; };
enum abc { ZZZ };

static xyz b;
abc c;

we used to produce:

t2.c:4:8: error: unknown type name 'xyz'
static xyz b;
       ^
t2.c:5:1: error: unknown type name 'abc'
abc c;
^

we now produce:

t2.c:4:8: error: use of tagged type 'xyz' without 'struct' tag
static xyz b;
       ^
       struct
t2.c:5:1: error: use of tagged type 'abc' without 'enum' tag
abc c;
^
enum

GCC produces the normal:
t2.c:4: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘b’
t2.c:5: error: expected ‘=’, ‘,’, ‘;’, ‘asm’ or ‘__attribute__’ before ‘c’

rdar://6783347

llvm-svn: 68914