Add an insertPass API to TargetPassConfig.  <rdar://problem/11498613>

Besides adding the new insertPass function, this patch uses it to
enhance the existing -print-machineinstrs so that the MachineInstrs
after a specific pass can be printed.

Patch by Bin Zeng!

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@157655 91177308-0d34-0410-b5e6-96231b3b80d8
diff --git a/lib/CodeGen/CodeGen.cpp b/lib/CodeGen/CodeGen.cpp
index a81bb5c..6548713 100644
--- a/lib/CodeGen/CodeGen.cpp
+++ b/lib/CodeGen/CodeGen.cpp
@@ -66,6 +66,7 @@
   initializeUnreachableMachineBlockElimPass(Registry);
   initializeVirtRegMapPass(Registry);
   initializeLowerIntrinsicsPass(Registry);
+  initializeMachineFunctionPrinterPassPass(Registry);
 }
 
 void LLVMInitializeCodeGen(LLVMPassRegistryRef R) {