to return Ref if the left callsite only reads memory read or written
by the right callsite; fix BasicAliasAnalysis to implement this.
Add AliasAnalysisEvaluator support for testing the two-callsite
form of getModRefInfo.
git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@110270 91177308-0d34-0410-b5e6-96231b3b80d8