Thread const correctness through a bunch of AliasAnalysis interfaces and

Thread const correctness through a bunch of AliasAnalysis interfaces and
eliminate several const_casts.

Make CallSite implicitly convertible to ImmutableCallSite.

Rename the getModRefBehavior for intrinsic IDs to
getIntrinsicModRefBehavior to avoid overload ambiguity with CallSite,
which happens to be implicitly convertible to bool.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110155 91177308-0d34-0410-b5e6-96231b3b80d8