Added a SetData() method to ValueObject. This

lets a ValueObject's contents be set from raw
data.  This has certain limitations (notably,
registers can only be set to data that is as
large as the register) but will be useful for
the new Materializer.

I also exposed this interface through SBValue.
I have added a testcase that exercises various
special cases of SBValue::SetData().

llvm-svn: 179437