Prevent CMake from identifying Android as MinGW.

If we don't explicitly set the target CMake will ID the compiler using
the default target, causing MINGW to be defined when a Windows host is
used.

Test: added
Bug: android/ndk#1581
Bug: https://gitlab.kitware.com/cmake/cmake/-/issues/22647
Change-Id: I3c4829eefd4fad6fbe85709c0d045b5e595b7b8e

build/cmake/android.toolchain.cmake

@@ -268,6 +268,25 @@ endif()
 set(ANDROID_TOOLCHAIN_ROOT
   "${CMAKE_ANDROID_NDK}/toolchains/llvm/prebuilt/${ANDROID_HOST_TAG}")
 
+# If we don't explicitly set the target CMake will ID the compiler using the
+# default target, causing MINGW to be defined when a Windows host is used.
+# https://github.com/android/ndk/issues/1581
+# https://gitlab.kitware.com/cmake/cmake/-/issues/22647
+if(CMAKE_ANDROID_ARCH_ABI STREQUAL armeabi-v7a)
+  set(ANDROID_LLVM_TRIPLE armv7-none-linux-androideabi)
+elseif(CMAKE_ANDROID_ARCH_ABI STREQUAL arm64-v8a)
+  set(ANDROID_LLVM_TRIPLE aarch64-none-linux-android)
+elseif(CMAKE_ANDROID_ARCH_ABI STREQUAL x86)
+  set(ANDROID_LLVM_TRIPLE i686-none-linux-android)
+elseif(CMAKE_ANDROID_ARCH_ABI STREQUAL x86_64)
+  set(ANDROID_LLVM_TRIPLE x86_64-none-linux-android)
+else()
+  message(FATAL_ERROR "Invalid Android ABI: ${ANDROID_ABI}.")
+endif()
+set(CMAKE_ASM_COMPILER_TARGET "${ANDROID_LLVM_TRIPLE}${CMAKE_SYSTEM_VERSION}")
+set(CMAKE_C_COMPILER_TARGET "${ANDROID_LLVM_TRIPLE}${CMAKE_SYSTEM_VERSION}")
+set(CMAKE_CXX_COMPILER_TARGET "${ANDROID_LLVM_TRIPLE}${CMAKE_SYSTEM_VERSION}")
+
 # NB: This variable causes CMake to automatically pass --sysroot to the
 # toolchain. Studio currently relies on this to recognize Android builds. If
 # this variable is removed, ensure that flag is still passed.

docs/changelogs/Changelog-r23.md

@@ -47,13 +47,21 @@ For Android Studio issues, follow the docs on the [Android Studio site].
 * [Issue 1573]: Fixed `ANDROID_USE_LEGACY_TOOLCHAIN_FILE` not being obeyed
   during CMake try-compile.
 * [Issue 1569]: Fixed `-fno-integrated-as` not being able to find the assembler.
-
+* [Issue 1581]: Added workaround for [CMake Issue 22647], which was causing
+  `MINGW` to be incorrectly defined by CMake when building for Android on a
+  Windows host. This only affected those using the Android toolchain file when
+  CMake 3.21 or newer was used. This likely was not a regression for users not
+  using the Android toolchain, and the workaround only affects toolchain file
+  users.
+
+[CMake Issue 22647]: https://gitlab.kitware.com/cmake/cmake/-/issues/22647
 [Issue 1536]: https://github.com/android/ndk/issues/1536
 [Issue 1544]: https://github.com/android/ndk/issues/1544
 [Issue 1553]: https://github.com/android/ndk/issues/1553
 [Issue 1560]: https://github.com/android/ndk/issues/1560
 [Issue 1573]: https://github.com/android/ndk/issues/1573
 [Issue 1569]: https://github.com/android/ndk/issues/1569
+[Issue 1581]: https://github.com/android/ndk/issues/1581
 
 ## Changes
 

tests/build/cmake_not_mingw/CMakeLists.txt

@@ -0,0 +1,6 @@
+cmake_minimum_required(VERSION 3.6)
+project(CMakeNotMinGW ASM C CXX)
+
+if(DEFINED MINGW)
+  message(FATAL_ERROR "MINGW should not be defined")
+endif()