Add support for sparcv9 targets.

The SPARC v8 and SPARC v8 architectures are very similar, so use a base
class to share most information between them.

Include operating systems with known SPARC v9 ports.

Also fix two issues with the SPARC v8 data layout string: SPARC v8 is a
big endian target with a 64-bit aligned stack.

llvm-svn: 179596