Revert "CalculateSpillWeights does not need to be a pass"

Temporarily revert my previous commit until I understand why it breaks 3 target tests.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@194272 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CodeGen.cpp b/lib/CodeGen/CodeGen.cpp
index 7430c53..920a48e 100644
--- a/lib/CodeGen/CodeGen.cpp
+++ b/lib/CodeGen/CodeGen.cpp
@@ -22,6 +22,7 @@
 void llvm::initializeCodeGen(PassRegistry &Registry) {
   initializeBasicTTIPass(Registry);
   initializeBranchFolderPassPass(Registry);
+  initializeCalculateSpillWeightsPass(Registry);
   initializeDeadMachineInstructionElimPass(Registry);
   initializeEarlyIfConverterPass(Registry);
   initializeExpandPostRAPass(Registry);