[CFLAA] Add more offset-sensitivity tracking.

This patch teaches FunctionInfo about offsets.

Like the last patch, this one doesn't introduce any visible
functionality change (the core algorithm knows nothing about offsets;
they're just plumbed through). Tests will come when we start acting
differently because of the offsets.

Patch by Jia Chen.

(N.B. I made a tiny change to Jia's patch to avoid warnings by GCC: I
put DenseMapInfo specializations in the `llvm` namespace. Only realized
that those appeared when compiling locally. :) )

Differential Revision: https://reviews.llvm.org/D22634

llvm-svn: 276486
diff --git a/llvm/lib/Analysis/CFLSteensAliasAnalysis.cpp b/llvm/lib/Analysis/CFLSteensAliasAnalysis.cpp
index d816822..9b21154 100644
--- a/llvm/lib/Analysis/CFLSteensAliasAnalysis.cpp
+++ b/llvm/lib/Analysis/CFLSteensAliasAnalysis.cpp
@@ -153,7 +153,7 @@
       if (Itr != InterfaceMap.end()) {
         if (CurrValue != Itr->second)
           Summary.RetParamRelations.push_back(
-              ExternalRelation{CurrValue, Itr->second});
+              ExternalRelation{CurrValue, Itr->second, UnknownOffset});
         break;
       }