Define common Android platforms.

Users can use these by adding `--android_platforms=@rules_android//:armeabi-v7a` to their builds (replacing `@rules_android` with the name they use to import https://github.com/bazelbuild/rules_android).

This is work towards enabling platforms and toolchains for Android builds (bazelbuild/bazel#16285).

PiperOrigin-RevId: 499992246
Change-Id: If03f275cb8372cd18a7cd21a94f693ebcc3dd569

BUILD

@@ -1,4 +1,41 @@
 load("@bazel_gazelle//:def.bzl", "gazelle")
 
+package(default_visibility = ["//visibility:public"])
+
 # gazelle:prefix github.com/bazelbuild/rules_android
 gazelle(name = "gazelle")
+
+# Common default platform definitions for use by Android projects.
+
+platform(
+    name = "x86",
+    constraint_values = [
+        "@platforms//os:android",
+        "@platforms//cpu:x86_32",
+    ],
+)
+
+platform(
+    name = "x86_64",
+    constraint_values = [
+        "@platforms//os:android",
+        "@platforms//cpu:x86_64",
+    ],
+)
+
+platform(
+    name = "armeabi-v7a",
+    constraint_values = [
+        "@platforms//os:android",
+        "@platforms//cpu:armv7",
+    ],
+)
+
+platform(
+    name = "arm64-v8a",
+    constraint_values =
+        [
+            "@platforms//cpu:arm64",
+            "@platforms//os:android",
+        ],
+)