Change a couple of the Parser::Diag methods to return DiagnosticInfo

Change a couple of the Parser::Diag methods to return DiagnosticInfo
and let the clients push whatever they want into the DiagnosticInfo
instead of hard coding a few forms.  Also switch various clients to
use Diag(Tok, ...) instead of Diag(Tok.getLocation(), ...) as the
canonical form to simplify the code a bit.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@59509 91177308-0d34-0410-b5e6-96231b3b80d8