Update NEON compiler flags for Skia to use the SK_ prefix.

skia/BUILD.gn

Index: skia/BUILD.gn
diff --git a/skia/BUILD.gn b/skia/BUILD.gn
index 162a0531caa915073bcdb1b915b6dd472793a418..67862921a65c66d7d323799d33076d8ae04ddd04 100644
--- a/skia/BUILD.gn
+++ b/skia/BUILD.gn
@@ -182,10 +182,10 @@ config("skia_library_config") {
 
   if (cpu_arch == "arm") {
     if (arm_use_neon) {
-      defines += [ "__ARM_HAVE_NEON" ]
+      defines += [ "SK_ARM_HAS_NEON", "__ARM_HAVE_NEON" ]
     }
     if (arm_optionally_use_neon) {
-      defines += [ "__ARM_HAVE_OPTIONAL_NEON_SUPPORT" ]
+      defines += [ "SK_ARM_HAS_OPTIONAL_NEON", "__ARM_HAVE_OPTIONAL_NEON_SUPPORT" ]
     }
   }