Add a RenderScript language type

Summary:
Add RenderScript language type and associate it with ".rs" extensions.
Test that the driver passes "-x renderscript" to the frontend for ".rs"
files.

(Also add '.rs' to the list of suffixes tested by lit).

Reviewers: rsmith

Subscribers: cfe-commits, srhines

Differential Revision: http://reviews.llvm.org/D21199

llvm-svn: 272317