Change PathDiagnosticPieces to be reference counted (simplifying their management), and introduce 'PathPieces' as a common container for PathDiagnosticPieces.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@150054 91177308-0d34-0410-b5e6-96231b3b80d8
6 files changed