[PM] Make the AnalysisManager parameter to run methods a reference.

This was originally a pointer to support pass managers which didn't use
AnalysisManagers. However, that doesn't realistically come up much and
the complexity of supporting it doesn't really make sense.

In fact, *many* parts of the pass manager were just assuming the pointer
was never null already. This at least makes it much more explicit and
clear.

llvm-svn: 263219
diff --git a/llvm/lib/Analysis/CallGraph.cpp b/llvm/lib/Analysis/CallGraph.cpp
index 2de2e0d..7d9252f 100644
--- a/llvm/lib/Analysis/CallGraph.cpp
+++ b/llvm/lib/Analysis/CallGraph.cpp
@@ -263,8 +263,8 @@
 char CallGraphAnalysis::PassID;
 
 PreservedAnalyses CallGraphPrinterPass::run(Module &M,
-                                            AnalysisManager<Module> *AM) {
-  AM->getResult<CallGraphAnalysis>(M).print(OS);
+                                            AnalysisManager<Module> &AM) {
+  AM.getResult<CallGraphAnalysis>(M).print(OS);
   return PreservedAnalyses::all();
 }