[ARM] Work around Clang 9 after MCCFIInstruction::OpType uses uint8_t

ARMAsmBackend.cpp:1205:57: error: use of overloaded operator '<<' is ambiguous (with operand types 'llvm::raw_ostream' and
 'llvm::MCCFIInstruction::OpType')
                             "unwind encoding, opcode=" << Inst.getOperation()
                             ~~~~~~~~~~~~~~~~~~~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~

Author: MaskRay

llvm/lib/Target/ARM/MCTargetDesc/ARMAsmBackend.cpp

@@ -1202,8 +1202,8 @@ uint32_t ARMAsmBackendDarwin::generateCompactUnwindEncoding(
       DEBUG_WITH_TYPE("compact-unwind",
                       llvm::dbgs()
                           << "CFI directive not compatible with compact "
-                             "unwind encoding, opcode=" << Inst.getOperation()
-                          << "\n");
+                             "unwind encoding, opcode="
+                          << uint8_t(Inst.getOperation()) << "\n");
       return CU::UNWIND_ARM_MODE_DWARF;
       break;
     }