Orderfile: enable code ordering for arm64 architectures.

This will enable prefetching on arm64. This doesn't matter now as it's
not deployed, but makes the build system less crufty (see
crbug.com/880425 as well).

Tested: confirmed by manual log examination that prefetch happened.
Bug: 874885, 880425
Change-Id: I2a962003df78d135bce783d0a9ad66b1b1ef290a
TBR: agrieve@chromium.org
Reviewed-on: https://chromium-review.googlesource.com/1206475
Commit-Queue: Matthew Cary <mattcary@chromium.org>
Reviewed-by: Benoit L <lizeb@chromium.org>
Reviewed-by: Egor Pasko <pasko@chromium.org>
Cr-Commit-Position: refs/heads/master@{#589112}

base/BUILD.gn

@@ -1919,7 +1919,7 @@ buildflag_header("synchronization_buildflags") {
 buildflag_header("anchor_functions_buildflags") {
   header = "anchor_functions_buildflags.h"
   header_dir = "base/android/library_loader"
-  _supports_code_ordering = current_cpu == "arm"
+  _supports_code_ordering = current_cpu == "arm" || current_cpu == "arm64"
 
   flags = [
     "USE_LLD=$use_lld",