Port android_relocation_packer_unittests to GN

BUG=510485

Review URL: https://codereview.chromium.org/1415803005

Cr-Commit-Position: refs/heads/master@{#356975}
diff --git a/BUILD.gn b/BUILD.gn
index 7cc7b5d..8a6bb8d 100644
--- a/BUILD.gn
+++ b/BUILD.gn
@@ -291,6 +291,10 @@
       ]
     }
 
+    if (target_cpu != "x64") {
+      deps += [ "//third_party/android_platform:android_relocation_packer_unittests($host_toolchain)" ]
+    }
+
     if (has_chrome_android_internal) {
       deps += [ "//clank" ]  # TODO(GYP) ??
     }