[GN] Add support for disabling opts via SK_BUILD_NO_OPTS define.

include/core/SkPreConfig.h

Index: include/core/SkPreConfig.h
diff --git a/include/core/SkPreConfig.h b/include/core/SkPreConfig.h
index b9b46c073a85736d739cb8ed4bf380789130c97f..928c1bda639379df2846aa10a7eb02110bfa734d 100644
--- a/include/core/SkPreConfig.h
+++ b/include/core/SkPreConfig.h
@@ -118,8 +118,12 @@
 #define SK_CPU_SSE_LEVEL_AVX      51
 #define SK_CPU_SSE_LEVEL_AVX2     52
 
-#ifdef SK_BUILD_FOR_IOS
-    #define SK_CPU_SSE_LEVEL 0  // We're tired of fighting with opts/ and iOS simulator.
+// When targetting iOS and using gyp to generate the build files, it is not
+// possible to select files to build depending on the architecture (i.e. it
+// is not possible to use hand optimized assembly implementation). In that
+// configuration SK_BUILD_NO_OPTS is defined. Remove optimisation then.
+#ifdef SK_BUILD_NO_OPTS
+    #define SK_CPU_SSE_LEVEL 0
 #endif
 
 // Are we in GCC?
@@ -190,14 +194,12 @@
     #endif
 #endif
 
-// Disable ARM64 optimizations for iOS due to complications regarding gyp and iOS.
-#if defined(__aarch64__) && !defined(SK_BUILD_FOR_IOS)
+#if defined(__aarch64__) && !defined(SK_BUILD_NO_OPTS)
     #define SK_CPU_ARM64
 #endif
 
 // All 64-bit ARM chips have NEON.  Many 32-bit ARM chips do too.
-// TODO: Why don't we want NEON on iOS?
-#if !defined(SK_ARM_HAS_NEON) && !defined(SK_BUILD_FOR_IOS) && (defined(__ARM_NEON__) || defined(__ARM_NEON))
+#if !defined(SK_ARM_HAS_NEON) && !defined(SK_BUILD_NO_OPTS) && (defined(__ARM_NEON__) || defined(__ARM_NEON))
     #define SK_ARM_HAS_NEON
 #endif