The count() function for STL datatypes returns unsigned, even
where it's only bool-like 1/0 result like std::set.count().

Some of the LLVM ADT already return unsigned count(), while
others return bool count().

This patch modifies SmallPtrSet, SmallSet, SparseSet count()
to return unsigned instead of bool:

 1 instead of true
 0 instead of false

More ADT to follow.