Set asmflags when building for iOS.
Set asmflags when building for iOS.

It's probably best we build iOS assembly with the iOS SDK and the right
architecture settings in Clang...

Change-Id: I68119641b1f86267ca85434b5a7f6ed37838ce23
Reviewed-on: https://skia-review.googlesource.com/8680
Reviewed-by: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@chromium.org>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@chromium.org>

HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,rubenvb/skia,google/skia,rubenvb/skia,rubenvb/skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,google/skia,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,HalCanary/skia-hc,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc,rubenvb/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,aosp-mirror/platform_external_skia,rubenvb/skia,aosp-mirror/platform_external_skia,Hikari-no-Tenshi/android_external_skia,rubenvb/skia,rubenvb/skia,rubenvb/skia,google/skia,Hikari-no-Tenshi/android_external_skia,google/skia,google/skia,rubenvb/skia,google/skia,google/skia,google/skia,rubenvb/skia,google/skia,google/skia,Hikari-no-Tenshi/android_external_skia,HalCanary/skia-hc