Introduce ImmutableCallSite, useful for contexts where no mutation

is necessary. Inherits from new templated baseclass CallSiteBase<>
which is highly customizable. Base CallSite on it too, in a configuration
that allows full mutation.
Adapt some call sites in analyses to employ ImmutableCallSite.


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@100100 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Transforms/Scalar/SCCP.cpp

@@ -1717,7 +1717,7 @@ static bool AddressIsTaken(const GlobalValue *GV) {
         return true;  // Storing addr of GV.
     } else if (isa<InvokeInst>(U) || isa<CallInst>(U)) {
       // Make sure we are calling the function, not passing the address.
-      CallSite CS((Instruction*)U);
+      ImmutableCallSite CS(cast<Instruction>(U));
       if (!CS.isCallee(UI))
         return true;
     } else if (const LoadInst *LI = dyn_cast<LoadInst>(U)) {