SymbolReaper::isLive(SymbolRef) now always returns true for SymbolRegionRvalues becau...

SymbolReaper::isLive(SymbolRef) now always returns true for SymbolRegionRvalues because these represent the symbolic values for parameters/globals upon entry to the function.  These values are always ;live' because they represent constraints on the context of how the function was called.  This will be useful for both summary generation but is also necessary to get RegionStore's lazy-binding of locations to symbols to work in practice with RemoveDeadBindings.

git-svn-id: https://llvm.org/svn/llvm-project/cfe/trunk@62771 91177308-0d34-0410-b5e6-96231b3b80d8