Add a MachinePostDominator pass

This is used in the AMDIL and R600 backends.

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@164029 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CodeGen.cpp b/lib/CodeGen/CodeGen.cpp
index 65f0941..a53f6f8 100644
--- a/lib/CodeGen/CodeGen.cpp
+++ b/lib/CodeGen/CodeGen.cpp
@@ -41,6 +41,7 @@
   initializeMachineCopyPropagationPass(Registry);
   initializeMachineCSEPass(Registry);
   initializeMachineDominatorTreePass(Registry);
+  initializeMachinePostDominatorTreePass(Registry);
   initializeMachineLICMPass(Registry);
   initializeMachineLoopInfoPass(Registry);
   initializeMachineModuleInfoPass(Registry);