-Use an array of offsets for all preprocessed entities
-Get rid of the separate array of offsets for just macro definitions;
for references to macro definitions use an index inside the preprocessed
entities array.
-Deserialize each preprocessed entity lazily, at first request; not in bulk.
Paves the way for binary searching of preprocessed entities that will offer
efficiency and will simplify things on the libclang side a lot.
llvm-svn: 139809