Changed declarations from Attr to InheritableAttr as they are already being processed that way semantically.

Patch thanks to Dean Sutherland!  Reviewed by Eli Friedman.
Remove DIBuilder cache of variable TheCU and change the few
uses that wanted it. Also change the interface for createCompileUnit
to compensate. Fix comments that refer to TheCU as well.
Equal means ==, not !=. Thanks to Benjamin for catching.