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

runtime/vm/dart.cc

Index: runtime/vm/dart.cc
diff --git a/runtime/vm/dart.cc b/runtime/vm/dart.cc
index 8fa693d0203cebffe8b4dd3edbfac2dae073e34e..f4821e4592fedf34ef53c025776c70c81572db56 100644
--- a/runtime/vm/dart.cc
+++ b/runtime/vm/dart.cc
@@ -617,10 +617,12 @@ const char* Dart::FeaturesString(Snapshot::Kind kind) {
 
     // Generated code must match the host architecture and ABI.
 #if defined(TARGET_ARCH_ARM)
-#if defined(TARGET_OS_MACOS)
+#if defined(TARGET_ABI_IOS)
     buffer.AddString(" arm-ios");
-#else
+#elif defined(TARGET_ABI_EABI)
     buffer.AddString(" arm-eabi");
+#else
+#error Unknown ABI
 #endif
     buffer.AddString(TargetCPUFeatures::hardfp_supported() ? " hardfp"
                                                            : " softfp");