Parser: support Microsoft syntax for 'typename typedef'

Summary:
Transform the token sequence for:
typename typedef T U;

to:
typename T typedef U;

Raise a diagnostic when this happens but only if we succeeded handling
the typename.

Reviewers: rsmith, rnk

Reviewed By: rsmith

CC: cfe-commits

Differential Revision: http://llvm-reviews.chandlerc.com/D1433

llvm-svn: 189867