Fix reference binding of const lvalue references to bit-fields, which

requires a temporary. Previously, we were building an initialization
sequence that bound to the bit-field as if it were a real lvalue. Note
that we previously (and still) diagnose binding of non-const
references to bit-fields, as we should.

There's no real way to test that this code is correct, since reference
binding does not *currently* have any representation in the AST. This
fix should make it easier for that to happen, so I've verified this
fix with...

Added InitializationSequence::dump(), to print an initialization
sequence for debugging purposes.

llvm-svn: 94826