Added preliminary support for CompoundLiterals in the static analyzer:

Added preliminary support for CompoundLiterals in the static analyzer:

- GRExprEngine::VisitCompoundLiteral...
   (1) visits the initializer list (generating ExplodedNodes)
   (2) creates a CompoundMemRegion for the literal
   (3) creates a new state with the bound literal values using
       GRStateManager::BindCompoundLiteral

- GRStateManager::BindCompoundLiteral simply calls
  StoreManager::BindCompoundLiteral to get a new store and returns a persistent
  GRState with that store.

- BasicStore::BindCompoundLiteral simply returns the same store, as it
  doesn't handle field sensitivity

- RegionStore::BindCompoundLiteral currently fires an assert (pending discussion
  of how to best implement mappings for CompoundLiteralRegion).

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@58277 91177308-0d34-0410-b5e6-96231b3b80d8