Changes through out the parser and actions/ast interface to return top-level

declarations through the asm streamer.  For a testcase like:

int G;
int H, I, *J;
int func() {}

'clang -parse-print-ast' prints:

Read top-level decl: G
Read top-level decl: H
Read top-level decl: I
Read top-level decl: J
Read top-level decl: func

llvm-svn: 38992