bool bitfields

For "boolean" bitfields, we sometimes use "unsigned" and sometimes use "bool", e.g.:

$ grep ': 1;' *
...
Type.h: bool SubClassData : 1;
...
Type.h: unsigned NoReturn : 1;
...

I vaguely recall that we switched to using "unsigned" a while back for bitfields that were enums (I believe that enums are being treated as "signed" by Visual C++). Since these are bools, not enum, what should we be doing here? It would be nice to be consistent.

"bool" is the natural type for these flags, so I suggest we stick with it.

  - Doug