Fix CPU features detection and stack alignment assert on iOS

runtime/vm/os_macos.cc

Index: runtime/vm/os_macos.cc
diff --git a/runtime/vm/os_macos.cc b/runtime/vm/os_macos.cc
index aed5d33529bbc28a7e0268d76fc87dd3d80853e6..eff65b9d52974fe806c8cd1944beb3a8d9b58c19 100644
--- a/runtime/vm/os_macos.cc
+++ b/runtime/vm/os_macos.cc
@@ -141,9 +141,17 @@ void OS::AlignedFree(void* ptr) {
 
 
 intptr_t OS::ActivationFrameAlignment() {
+#if TARGET_OS_IOS
+#if TARGET_ARCH_ARM
+  return 8;

[rmacnak, 2015/10/27 20:44:22]

// Even if we generate code that maintains a strong alignment, we cannot assert
the stronger stack alignment because C++ code will not maintain it.

[Chinmay, 2015/10/27 20:49:47]

ack

+#elif TARGET_ARCH_ARM64
+  return 16;
+#endif
+#else  // TARGET_OS_IOS
   // OS X activation frames must be 16 byte-aligned; see "Mac OS X ABI
   // Function Call Guide".
   return 16;
+#endif  // TARGET_OS_IOS
 }