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 (#120326).

Update to the current LTS NDK 26, and to its minimum supported API 21.

Fixes: #120567

config.example.toml

@@ -395,7 +395,7 @@
 #metrics = false
 
 # Specify the location of the Android NDK. Used when targeting Android.
-#android-ndk = "/path/to/android-ndk-r25b"
+#android-ndk = "/path/to/android-ndk-r26d"
 
 # =============================================================================
 # General install configuration options

src/bootstrap/src/utils/cc_detect.rs

@@ -247,18 +247,16 @@ 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 r26d 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.
         "darwin-x86_64"
     } else if cfg!(target_os = "windows") {
         "windows-x86_64"
     } else {
-        // NDK r25b only has official releases for macOS, Windows and Linux.
+        // NDK r26d only has official releases for macOS, Windows and Linux.
         // Try the Linux directory everywhere else, on the assumption that the OS has an
         // emulation layer that can cope (e.g. BSDs).
         "linux-x86_64"

src/bootstrap/src/utils/change_tracker.rs

@@ -210,4 +210,9 @@ pub const CONFIG_CHANGE_HISTORY: &[ChangeInfo] = &[
         severity: ChangeSeverity::Info,
         summary: "the `wasm-component-ld` tool is now built as part of `build.extended` and can be a member of `build.tools`",
     },
+    ChangeInfo {
+        change_id: 120593,
+        severity: ChangeSeverity::Info,
+        summary: "Removed android-ndk r25b support in favor of android-ndk r26d.",
+    },
 ];

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

@@ -6,7 +6,7 @@ RUN sh /scripts/android-base-apt-get.sh
 
 COPY scripts/android-ndk.sh /scripts/
 RUN . /scripts/android-ndk.sh && \
-    download_ndk android-ndk-r25b-linux.zip
+    download_ndk android-ndk-r26d-linux.zip
 
 RUN dpkg --add-architecture i386 && \
     apt-get update && \

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

@@ -1,6 +1,6 @@
 emulator emulator-linux-5264690.zip 48c1cda2bdf3095d9d9d5c010fbfb3d6d673e3ea
 patcher;v4 3534162-studio.sdk-patcher.zip 046699c5e2716ae11d77e0bad814f7f33fab261e
-platform-tools platform-tools_r28.0.2-linux.zip 46a4c02a9b8e4e2121eddf6025da3c979bf02e28
-platforms;android-18 android-18_r03.zip e6b09b3505754cbbeb4a5622008b907262ee91cb
-system-images;android-18;default;armeabi-v7a sys-img/android/armeabi-v7a-18_r05.zip 580b583720f7de671040d5917c8c9db0c7aa03fd
+platform-tools platform-tools_r34.0.5-linux.zip 96097475cf7b279fdd8f218f5d043ffe94104ec3
+platforms;android-21 android-21_r02.zip 53536556059bb29ae82f414fd2e14bc335a4eb4c
+system-images;android-21;default;armeabi-v7a sys-img/android/armeabi-v7a-21_r04.zip 8c606f81306564b65e41303d2603e4c42ded0d10
 tools sdk-tools-linux-4333796.zip 8c7c28554a32318461802c1291d76fccfafde054

src/ci/docker/host-x86_64/dist-android/Dockerfile

@@ -6,7 +6,7 @@ RUN sh /scripts/android-base-apt-get.sh
 # ndk
 COPY scripts/android-ndk.sh /scripts/
 RUN . /scripts/android-ndk.sh && \
-    download_ndk android-ndk-r25b-linux.zip
+    download_ndk android-ndk-r26d-linux.zip
 
 # env
 ENV TARGETS=arm-linux-androideabi