Rename AttributeSetImpl::NumAttrs and AttributeSetImpl::getNumAttributes to reflect that they work on slots rather than attributes. NFC

Summary: The current naming not only doesn't convey the meaning of what this does, but worse, it convey the wrong meaning. This was a major source of confusion understanding the code, so I'm applying the boy scout rule here and making it better after I leave.

Reviewers: void, bkramer, whitequark

Differential Revision: http://reviews.llvm.org/D21264

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@272725 91177308-0d34-0410-b5e6-96231b3b80d8
2 files changed