[ARM][Thumb][FIX] Add unwinding information to t4

[dnsampaio]

Summary

Add missing part of patch D71361. Now that the stack-frame
can be operated using a addw/subw instruction, they should
appear in the unwinding list.

[dmgreen]

Sounds good. Can you add a test?

[dnsampaio]

Added test

[dmgreen]

Thanks. LGTM

llvm/lib/Target/ARM/ARMAsmPrinter.cpp

if (SrcReg == ARM::SP) {
         MI->print(errs());
         llvm_unreachable("Unsupported opcode for unwinding information");
       case ARM::MOVr:
       case ARM::tMOVr:
         Offset = 0;
         break;
       case ARM::ADDri:
       case ARM::t2ADDri:
+      case ARM::t2ADDri12:
         Offset = -MI->getOperand(2).getImm();
         break;
       case ARM::SUBri:
       case ARM::t2SUBri:
+      case ARM::t2SUBri12:
         Offset = MI->getOperand(2).getImm();
         break;
       case ARM::tSUBspi:
         Offset = MI->getOperand(2).getImm()*4;
         break;
       case ARM::tADDspi:
       case ARM::tADDrSPi:
         Offset = -MI->getOperand(2).getImm()*4;