Revert to old behavior regarding SK_CPU_ARM and update documentation around SK_CPU_ARM64 on iOS.

include/core/SkPreConfig.h

 
 /*
  * Copyright 2006 The Android Open Source Project
  *
  * Use of this source code is governed by a BSD-style license that can be
  * found in the LICENSE file.
  */
 
 
 #ifndef SkPreConfig_DEFINED
@@ skipping 131 matching lines @@
             #define SK_CPU_SSE_LEVEL    SK_CPU_SSE_LEVEL_SSE2
         #elif _M_IX86_FP == 1
             #define SK_CPU_SSE_LEVEL    SK_CPU_SSE_LEVEL_SSE1
         #endif
     #endif
 #endif
 
 //////////////////////////////////////////////////////////////////////
 // ARM defines
 
-#if defined(__arm__) && !defined(__APPLE__)
+#if defined(__arm__) && (!defined(__APPLE__) || !TARGET_IPHONE_SIMULATOR)
     #define SK_CPU_ARM
 
     #if defined(__GNUC__)
         #if defined(__ARM_ARCH_7__) || defined(__ARM_ARCH_7A__) \
                 || defined(__ARM_ARCH_7R__) || defined(__ARM_ARCH_7M__) \
                 || defined(__ARM_ARCH_7EM__) || defined(_ARM_ARCH_7)
             #define SK_ARM_ARCH 7
         #elif defined(__ARM_ARCH_6__) || defined(__ARM_ARCH_6J__) \
                 || defined(__ARM_ARCH_6K__) || defined(__ARM_ARCH_6Z__) \
                 || defined(__ARM_ARCH_6ZK__) || defined(__ARM_ARCH_6T2__) \
@@ skipping 10 matching lines @@
         #endif
 
         #if defined(__thumb2__) && (SK_ARM_ARCH >= 6) \
                 || !defined(__thumb__) && ((SK_ARM_ARCH > 5) || defined(__ARM_ARCH_5E__) \
                 || defined(__ARM_ARCH_5TE__) || defined(__ARM_ARCH_5TEJ__))
             #define SK_ARM_HAS_EDSP
         #endif
     #endif
 #endif
 
-#if defined(__aarch64__) && !defined(__APPLE__)
+// Disable ARM64 optimizations for iOS due to complications regarding gyp and iOS.
+#if defined(__aarch64__) && !defined(SK_BUILD_FOR_IOS)
     #define SK_CPU_ARM64
 #endif
 
 //////////////////////////////////////////////////////////////////////
 
 #if !defined(SKIA_IMPLEMENTATION)
     #define SKIA_IMPLEMENTATION 0
 #endif
 
 #if defined(SKIA_DLL)
@@ skipping 48 matching lines @@
  *
  * NOTE: Clang/ARM (r161757) does not support the 'optimize' attribute.
  */
 #if SK_HAS_ATTRIBUTE(optimize)
 #   define SK_ATTRIBUTE_OPTIMIZE_O1 __attribute__((optimize("O1")))
 #else
 #   define SK_ATTRIBUTE_OPTIMIZE_O1 /* nothing */
 #endif
 
 #endif