Set TARGET_OS_* from GN, falling back to HOST_OS_*.

runtime/vm/stub_code_arm.cc

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 #include "vm/globals.h"
 #if defined(TARGET_ARCH_ARM)
 
 #include "vm/assembler.h"
 #include "vm/code_generator.h"
 #include "vm/cpu.h"
@@ skipping 796 matching lines @@
   // Save top resource and top exit frame info. Use R4-6 as temporary registers.
   // StackFrameIterator reads the top exit frame info saved in this frame.
   __ LoadFromOffset(kWord, R9, THR, Thread::top_exit_frame_info_offset());
   __ LoadFromOffset(kWord, R4, THR, Thread::top_resource_offset());
   __ LoadImmediate(R8, 0);
   __ StoreToOffset(kWord, R8, THR, Thread::top_resource_offset());
   __ StoreToOffset(kWord, R8, THR, Thread::top_exit_frame_info_offset());
 
   // kExitLinkSlotFromEntryFp must be kept in sync with the code below.
   __ Push(R4);
-#if defined(TARGET_ABI_IOS)
+#if defined(TARGET_OS_MACOS) || TARGET_OS_IOS
   ASSERT(kExitLinkSlotFromEntryFp == -26);
-#elif defined(TARGET_ABI_EABI)
+#else
   ASSERT(kExitLinkSlotFromEntryFp == -27);
 #endif
   __ Push(R9);
 
   // Load arguments descriptor array into R4, which is passed to Dart code.
   __ ldr(R4, Address(R1, VMHandles::kOffsetOfRawPtrInHandle));
 
   // Load number of arguments into R9.
   __ ldr(R9, FieldAddress(R4, ArgumentsDescriptor::count_offset()));
   __ SmiUntag(R9);
@@ skipping 1456 matching lines @@
 }
 
 
 void StubCode::GenerateAsynchronousGapMarkerStub(Assembler* assembler) {
   __ bkpt(0);
 }
 
 }  // namespace dart
 
 #endif  // defined TARGET_ARCH_ARM