Update Android testing to API 21, matching NDK 26

We were running testing on API 18, which was already out of support for
NDK 25, and some of the ancient behavior in that image was causing
trouble when developing `rustc` features (rust-lang#120326).

We'll be updating to NDK 26 (latest LTS) shortly, so rather than
updating to API 19, then again to API 21 in a bit, just jump straight
to 21.

Fixes: rust-lang#120567

.github/workflows/ci.yml

@@ -204,7 +204,7 @@ jobs:
               - self-hosted
               - ARM64
               - linux
-          - name: arm-android
+          - name: aarch64-android
             os: ubuntu-20.04-8core-32gb
             env: {}
           - name: armhf-gnu

src/bootstrap/src/utils/cc_detect.rs

@@ -239,10 +239,8 @@ pub(crate) fn ndk_compiler(compiler: Language, triple: &str, ndk: &Path) -> Path
         triple.to_string()
     };
 
-    // API 19 is the earliest API level supported by NDK r25b but AArch64 and x86_64 support
-    // begins at API level 21.
-    let api_level =
-        if triple.contains("aarch64") || triple.contains("x86_64") { "21" } else { "19" };
+    // The earliest API supported by NDK r26b is 21.
+    let api_level = "21";
     let compiler = format!("{}{}-{}", triple_translated, api_level, compiler.clang());
     let host_tag = if cfg!(target_os = "macos") {
         // The NDK uses universal binaries, so this is correct even on ARM.

src/ci/docker/host-x86_64/arm-android/Dockerfile → src/ci/docker/host-x86_64/aarch64-android/Dockerfile

@@ -21,7 +21,7 @@ RUN dpkg --add-architecture i386 && \
 
 COPY scripts/android-sdk.sh /scripts/
 COPY scripts/android-sdk-manager.py /scripts/
-COPY host-x86_64/arm-android/android-sdk.lock /android/sdk/android-sdk.lock
+COPY host-x86_64/aarch64-android/android-sdk.lock /android/sdk/android-sdk.lock
 RUN /scripts/android-sdk.sh
 
 ENV PATH=$PATH:/android/sdk/emulator

src/ci/docker/host-x86_64/aarch64-android/android-sdk.lock

@@ -0,0 +1,6 @@
+emulator emulator-linux_x64-11237101.zip 0fd36dd5a7be6ee8770776a95c2933541d9243f3
+patcher;v4 3534162-studio.sdk-patcher.zip 046699c5e2716ae11d77e0bad814f7f33fab261e
+platform-tools platform-tools_r34.0.5-linux.zip 96097475cf7b279fdd8f218f5d043ffe94104ec3
+platforms;android-21 android-21_r02.zip 53536556059bb29ae82f414fd2e14bc335a4eb4c
+system-images;android-21;default;arm64-v8a sys-img/android/arm64-v8a-21_r04.zip c4375f1b4b4cd21a8617660e25f621cedcbd8332
+tools sdk-tools-linux-4333796.zip 8c7c28554a32318461802c1291d76fccfafde054

src/ci/github-actions/ci.yml

@@ -381,7 +381,7 @@ jobs:
           - name: aarch64-gnu
             <<: *job-aarch64-linux
 
-          - name: arm-android
+          - name: aarch64-android
             <<: *job-linux-8c
 
           - name: armhf-gnu