PassManager.h - remove unnecessary Function.h/Module.h includes. NFCI.

PassManager.h is one of the top headers in the ClangBuildAnalyzer frontend worst offenders list.

This exposes a large number of implicit dependencies on various forward declarations/includes in other headers that need addressing.
diff --git a/llvm/lib/CodeGen/MachineSizeOpts.cpp b/llvm/lib/CodeGen/MachineSizeOpts.cpp
index 584d43b..e19862e 100644
--- a/llvm/lib/CodeGen/MachineSizeOpts.cpp
+++ b/llvm/lib/CodeGen/MachineSizeOpts.cpp
@@ -12,9 +12,10 @@
 //===----------------------------------------------------------------------===//
 
 #include "llvm/CodeGen/MachineSizeOpts.h"
-#include "llvm/CodeGen/MBFIWrapper.h"
 #include "llvm/Analysis/ProfileSummaryInfo.h"
+#include "llvm/CodeGen/MBFIWrapper.h"
 #include "llvm/CodeGen/MachineBlockFrequencyInfo.h"
+#include "llvm/IR/Function.h"
 
 using namespace llvm;