Fix "use_libgav1_parser" assert for Windows on ARM64

Fixes assert when trying to generate ninja build files for Windows Arm64 platform.

Bug: 1157842
Change-Id: I3e1858696696537bb96b36d3969f9f7f355faa28
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2584813
Commit-Queue: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Reviewed-by: James Zern <jzern@google.com>
Cr-Commit-Position: refs/heads/master@{#836908}

third_party/libgav1/options.gni

@@ -10,5 +10,6 @@ declare_args() {
   enable_libgav1_decoder =
       is_ash && (target_cpu == "arm" || target_cpu == "arm64")
   use_libgav1_parser =
-      (is_ash || is_win) && (target_cpu == "x86" || target_cpu == "x64")
+      (is_ash || is_win) &&
+      (target_cpu == "x86" || target_cpu == "x64" || target_cpu == "arm64")
 }