C++17 compatibility: make WITH_TIDY=1 happy again.

Bug: http://b/111067277
Test: builds
Change-Id: I8b69ea3815e14bb6eb27f40c0dd01a85b340a355
diff --git a/compiler/optimizing/code_generator_arm_vixl.cc b/compiler/optimizing/code_generator_arm_vixl.cc
index d5b734d..dad1813 100644
--- a/compiler/optimizing/code_generator_arm_vixl.cc
+++ b/compiler/optimizing/code_generator_arm_vixl.cc
@@ -1037,26 +1037,26 @@
 size_t CodeGeneratorARMVIXL::SaveCoreRegister(size_t stack_index ATTRIBUTE_UNUSED,
                                               uint32_t reg_id ATTRIBUTE_UNUSED) {
   TODO_VIXL32(FATAL);
-  return 0;
+  UNREACHABLE();
 }
 
 // Restores the register from the stack. Returns the size taken on stack.
 size_t CodeGeneratorARMVIXL::RestoreCoreRegister(size_t stack_index ATTRIBUTE_UNUSED,
                                                  uint32_t reg_id ATTRIBUTE_UNUSED) {
   TODO_VIXL32(FATAL);
-  return 0;
+  UNREACHABLE();
 }
 
 size_t CodeGeneratorARMVIXL::SaveFloatingPointRegister(size_t stack_index ATTRIBUTE_UNUSED,
                                                        uint32_t reg_id ATTRIBUTE_UNUSED) {
   TODO_VIXL32(FATAL);
-  return 0;
+  UNREACHABLE();
 }
 
 size_t CodeGeneratorARMVIXL::RestoreFloatingPointRegister(size_t stack_index ATTRIBUTE_UNUSED,
                                                           uint32_t reg_id ATTRIBUTE_UNUSED) {
   TODO_VIXL32(FATAL);
-  return 0;
+  UNREACHABLE();
 }
 
 static void GenerateDataProcInstruction(HInstruction::InstructionKind kind,
@@ -2268,7 +2268,7 @@
     case DataType::Type::kUint64:
     case DataType::Type::kVoid:
       LOG(FATAL) << "Unexpected parameter type " << type;
-      break;
+      UNREACHABLE();
   }
   return Location::NoLocation();
 }