gh-146541: Allow building the Android testbed for 32-bit targets

This allows building the Android testbed for 32-bit targets using the prebuilt 32-bit dependencies that are already available here: https://github.com/beeware/cpython-android-source-deps/releases , adding the target triplets to match them, `arm-linux-androideabi` and `i686-linux-android`.

This also adds the `arm` key to the dictionary used to convert the `machine` variable to an Android ABI in `sysconfig.get_platform()`, because when the Android testbed is being cross-compiled, it stores the contents of the first substring of `_PYTHON_HOST_PLATFORM` before the first `-` symbol in the `machine` variable, which the dictionary does not currently handle.

Author: robertkirkman

Android/android.py

@@ -34,7 +34,7 @@
 TESTBED_DIR = ANDROID_DIR / "testbed"
 CROSS_BUILD_DIR = PYTHON_DIR / "cross-build"
 
-HOSTS = ["aarch64-linux-android", "x86_64-linux-android"]
+HOSTS = ["aarch64-linux-android", "x86_64-linux-android", "arm-linux-androideabi", "i686-linux-android"]
 APP_ID = "org.python.testbed"
 DECODE_ARGS = ("UTF-8", "backslashreplace")
 

Android/testbed/app/build.gradle.kts

@@ -16,6 +16,8 @@ val inSourceTree = (
 val KNOWN_ABIS = mapOf(
     "aarch64-linux-android" to "arm64-v8a",
     "x86_64-linux-android" to "x86_64",
+    "arm-linux-androideabi" to "armeabi-v7a",
+    "i686-linux-android" to "x86",
 )
 
 // Discover prefixes.

Lib/sysconfig/__init__.py

@@ -697,12 +697,16 @@ def get_platform():
         # When Python is running on 32-bit ARM Android on a 64-bit ARM kernel,
         # 'os.uname().machine' is 'armv8l'. Such devices run the same userspace
         # code as 'armv7l' devices.
+        # During the build process of the Android testbed when targeting 32-bit ARM,
+        # '_PYTHON_HOST_PLATFORM' is 'arm-linux-androideabi', so 'machine' becomes
+        # 'arm'.
         machine = {
             "x86_64": "x86_64",
             "i686": "x86",
             "aarch64": "arm64_v8a",
             "armv7l": "armeabi_v7a",
             "armv8l": "armeabi_v7a",
+            "arm": "armeabi_v7a",
         }[machine]
     elif osname == "linux":
         # At least on Linux/Intel, 'machine' is the processor --

Lib/test/test_sysconfig.py

@@ -376,6 +376,7 @@ def test_get_platform(self):
             'aarch64': 'arm64_v8a',
             'armv7l': 'armeabi_v7a',
             'armv8l': 'armeabi_v7a',
+            'arm': 'armeabi_v7a',
         }.items():
             with self.subTest(machine):
                 self._set_uname(('Linux', 'localhost', '3.18.91+',
@@ -585,6 +586,7 @@ def test_android_ext_suffix(self):
             "aarch64": "aarch64-linux-android",
             "armv7l": "arm-linux-androideabi",
             "armv8l": "arm-linux-androideabi",
+            "arm": "arm-linux-androideabi",
         }[machine]
         self.assertEndsWith(suffix, f"-{expected_triplet}.so")