Several fixes/simplifications surrounding how we stream top-level decl AST's.

The following code...

typedef struct cssm_data {} CSSM_DATA, *CSSM_DATA_PTR;

struct Y { int A; };

struct X { int A; } D; 

struct X E, F;

...now produces the following output...

> ../../Debug/bin/clang xx.c -ast-print
Read top-level tag decl: 'cssm_data'
typedef struct cssm_data CSSM_DATA;
typedef struct cssm_data *CSSM_DATA_PTR;
Read top-level tag decl: 'Y'
Read top-level tag decl: 'X'
Read top-level variable decl: 'D'
Read top-level variable decl: 'E'
Read top-level variable decl: 'F'

...which is much more accurate than the previous -ast-print output...

typedef struct cssm_data CSSM_DATA;
typedef struct cssm_data CSSM_DATA;
Read top-level variable decl: 'D'
Read top-level variable decl: 'E'
Read top-level variable decl: 'E'

llvm-svn: 44421