ARM implement TargetInstrInfo::getNoopForMachoTarget()

Without this hook, functions w/ a completely empty body (including no
epilogue) will cause an MCEmitter assertion failure.

For example,
define internal fastcc void @empty_function() {
  unreachable
}

rdar://10947471

git-svn-id: https://llvm.org/svn/llvm-project/llvm/trunk@151673 91177308-0d34-0410-b5e6-96231b3b80d8

lib/Target/ARM/Thumb2InstrInfo.h

@@ -28,6 +28,9 @@ class Thumb2InstrInfo : public ARMBaseInstrInfo {
 public:
   explicit Thumb2InstrInfo(const ARMSubtarget &STI);
 
+  /// getNoopForMachoTarget - Return the noop instruction to use for a noop.
+  void getNoopForMachoTarget(MCInst &NopInst) const;
+
   // Return the non-pre/post incrementing version of 'Opc'. Return 0
   // if there is not such an opcode.
   unsigned getUnindexedOpcode(unsigned Opc) const;