Clean up whitespace and indentation a bit


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173960 91177308-0d34-0410-b5e6-96231b3b80d8
Use the number of 'slots' in the AttributeSetImpl being 0 to indicate that the AttributeSet is empty.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@173962 91177308-0d34-0410-b5e6-96231b3b80d8