Don't assume we want the iOS ABI if running simarm on Mac and the EABI otherwise.

runtime/vm/disassembler_arm.cc

Index: runtime/vm/disassembler_arm.cc
diff --git a/runtime/vm/disassembler_arm.cc b/runtime/vm/disassembler_arm.cc
index 437bee8a183fe2d2a463460420ad940fe42d7c63..2b0c1038e58cf5e9c89e86b2e3e11959ada9737a 100644
--- a/runtime/vm/disassembler_arm.cc
+++ b/runtime/vm/disassembler_arm.cc
@@ -114,12 +114,14 @@ void ARMDecoder::PrintCondition(Instr* instr) {
 // formatting, except for register alias pp (r5).
 // See for example the command "objdump -d <binary file>".
 static const char* reg_names[kNumberOfCpuRegisters] = {
-#if defined(TARGET_OS_MACOS)
+#if defined(TARGET_ABI_IOS)
   "r0", "r1", "r2", "r3", "r4", "pp", "r6", "fp",
   "r8", "r9", "r10", "r11", "ip", "sp", "lr", "pc",
-#else
+#elif defined(TARGET_ABI_EABI)
   "r0", "r1", "r2", "r3", "r4", "pp", "r6", "r7",
   "r8", "r9", "r10", "fp", "ip", "sp", "lr", "pc",
+#else
+#error Unknown ABI
 #endif
 };