CompoundVal now uses an ImmutableList<SVal> to store its set of SVals.  This change was motivated by the need to allow state-splitting in GRExprEngine::VisitInitListExpr.  As a side-benefit, we no longer need to perform any copies of SVals when creating a CompoundSVal, and the profiling of CompoundSVal is now constant time.


git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@58437 91177308-0d34-0410-b5e6-96231b3b80d8