First chunk of MachineInstr bundle support.

1. Added opcode BUNDLE
2. Taught MachineInstr class to deal with bundled MIs
3. Changed MachineBasicBlock iterator to skip over bundled MIs; added an iterator to walk all the MIs
4. Taught MachineBasicBlock methods about bundled MIs


git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@145975 91177308-0d34-0410-b5e6-96231b3b80d8

utils/TableGen/CodeGenTarget.cpp

@@ -267,6 +267,7 @@ void CodeGenTarget::ComputeInstrsByEnum() const {
     "DBG_VALUE",
     "REG_SEQUENCE",
     "COPY",
+    "BUNDLE",
     0
   };
   const DenseMap<const Record*, CodeGenInstruction*> &Insts = getInstructions();