Emit the DWARF tag for the RenderScript language

Summary:
If the RenderScript LangOpt is set, either via '-x renderscript' or the '.rs'
file extension, set the DWARF language tag to be that of RenderScript.

Reviewers: rsmith

Subscribers: cfe-commits, srhines

Differential Revision: http://reviews.llvm.org/D21451

llvm-svn: 273321