Only use thread_local on aarch64 iOS build variants.
Only use thread_local on aarch64 iOS build variants.

Versions of iOS < 9.0 do no have thread_local support and simulator build
variants emit an error about this (even though they are x86_64). This patch
flips the logic to only enable thread_local usage on aarch64 build variants.

Change-Id: I63294be4f9a2bdb3bcd6d49b213e9c3326f50a5b
Reviewed-on: https://skia-review.googlesource.com/c/skia/+/234020
Auto-Submit: Chinmay Garde <2c5f961126c80cfe4f9b4f17931784885f34f766@google.com>
Commit-Queue: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>
Reviewed-by: Mike Klein <14574f09dfa9b4e14759b88c3426a495a0e627b0@google.com>

aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,google/skia,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,HalCanary/skia-hc,google/skia,google/skia,aosp-mirror/platform_external_skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,google/skia,google/skia,aosp-mirror/platform_external_skia,google/skia,HalCanary/skia-hc,aosp-mirror/platform_external_skia