Print registered targets in clang's version information

Summary:
Other llvm tools display their registered targets when showing version
information, but for some reason clang has never done this.

To support this, D33899 adds the llvm parts, which make it possible to
print version information to arbitrary raw_ostreams.  This change adds
a call to printRegisteredTargetsForVersion in clang's PrintVersion, and
adds a raw_ostream parameter to two other PrintVersion functions.

Reviewers: beanz, chandlerc, dberris, mehdi_amini, zturner

Reviewed By: mehdi_amini

Subscribers: cfe-commits

Differential Revision: https://reviews.llvm.org/D33900

llvm-svn: 304836