Updated the LLDB rvalue reference test to cross-reference with a bugzilla report,

provide more detail on compiler compatibility, and to illustrate that this is
an issue with expression evaluation.

- Note that clang doesn't emit DW_TAG_const_type, which might be okay if there's
no such thing as a non-const rvalue reference.  How about foo(make_int())?

llvm-svn: 187499