This change is motivated by the long-standing issue that most Linux distributions ship an outdated Gradle, which is often too old for modern Android builds. In typical Android projects this is solved by using the Gradle wrapper, which ensures a compatible Gradle version is downloaded and used automatically. However, Wine cannot rely on the Gradle wrapper for this purpose, and integrating automatic downloads into the build system is not acceptable, since the build process must not fetch external resources. As a result, Gradle and the Android SDK effectively become external prerequisites that must be provided by the user or by higher-level build scripts. Previously, missing or outdated dependencies would only surface later during the build, often resulting in confusing or hard-to-diagnose errors. This change makes these requirements explicit and enforces them at configure time: - `gradle` is detected, its version is checked, and the resolved path is cached. - `ANDROID_HOME` is required and validated against the expected SDK layout. - A minimal sanity check ensures that a usable `build-tools` installation is present. This allows the build to fail early with clear error messages if the environment is not properly set up, instead of failing deep inside the Gradle build. Additionally, `GRADLE` and `ANDROID_HOME` are cached by configure, so they do not need to be re-specified when invoking make or even present in environment. -- v5: wineandroid: print hint for full APK build when using dummy target configure: validate Android build environment using minimal Gradle project https://gitlab.winehq.org/wine/wine/-/merge_requests/10438