Reapply "Fix CMAKE_SYSTEM_PROCESSOR CMake use case."

With the test fixed for Windows (`ndk_path.as_posix()` to pass a path
with forward slashes instead of the normal Windows thing). Maybe. Won't
know until post-submit.

This reverts commit d4bfe343ef159b072ed1493d83908f19c977f0a3.

Bug: android/ndk#2049
Test: windows machine is FUBquickR, will let CI do it
(cherry picked from https://android-review.googlesource.com/q/commit:539c3e39f0111cdac00d6d0829b7c339c31c81ea)
Merged-In: Ic14f225d5b6af81547a49ee26e72fc2bd869256f
Change-Id: Ic14f225d5b6af81547a49ee26e72fc2bd869256f

docs/changelogs/Changelog-r27.md

@@ -31,8 +31,16 @@ directly, see the [build system maintainers guide].
 
 * [Issue 2039]: Fixed `LOCAL_STRIP_MODE` not being reset by
   `include $(CLEAR_VARS)`.
+* [Issue 2049]: Restored metadata used by CMake in non-toolchain-file use cases
+  that used `CMAKE_SYSTEM_PROCESSOR` instead of `CMAKE_ANDROID_ARCH_ABI`. If you
+  ran into this problem, you should switch to using `CMAKE_ANDROID_ARCH_ABI`
+  because that's what [CMake's docs] say to use. Better still, use the NDK's
+  [toolchain file].
 
 [Issue 2039]: https://github.com/android/ndk/issues/2039
+[Issue 2049]: https://github.com/android/ndk/issues/2049
+[CMake's docs]: https://cmake.org/cmake/help/latest/manual/cmake-toolchains.7.html#cross-compiling-for-android-with-the-ndk
+[toolchain file]: https://developer.android.com/ndk/guides/cmake
 
 ## Changes
 

ndk/checkbuild.py

@@ -1506,6 +1506,12 @@ def abis_meta_transform(metadata: dict[str, Any]) -> dict[str, Any]:
         abi_infos[f"NDK_ABI_{abi}_LLVM_TRIPLE"] = llvm_triple
         abi_infos[f"NDK_ABI_{abi}_MIN_OS_VERSION"] = int(abi_data["min_os_version"])
 
+        # These will appear to be unused because there is no reference to them anywhere
+        # in the code base, but they're used by CMake for non-toolchain-file users, so
+        # they must be preserved.
+        abi_infos[f"NDK_PROC_{proc}_ABI"] = abi
+        abi_infos[f"NDK_ARCH_{arch}_ABI"] = abi
+
     meta_vars = {
         "NDK_DEFAULT_ABIS": sorted(default_abis),
         "NDK_DEPRECATED_ABIS": sorted(deprecated_abis),

tests/build/cmake_without_toolchain_file/CMakeLists.txt

@@ -0,0 +1,4 @@
+cmake_minimum_required(VERSION 3.22.0)
+project(HelloWorld)
+
+add_library(foo SHARED foo.cpp)

tests/build/cmake_without_toolchain_file/foo.cpp

@@ -0,0 +1,2 @@
+extern "C" void foo() {
+}

tests/build/cmake_without_toolchain_file/test.py

@@ -0,0 +1,75 @@
+#
+# Copyright (C) 2024 The Android Open Source Project
+#
+# Licensed under the Apache License, Version 2.0 (the "License");
+# you may not use this file except in compliance with the License.
+# You may obtain a copy of the License at
+#
+#      http://www.apache.org/licenses/LICENSE-2.0
+#
+# Unless required by applicable law or agreed to in writing, software
+# distributed under the License is distributed on an "AS IS" BASIS,
+# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+# See the License for the specific language governing permissions and
+# limitations under the License.
+#
+"""Tests that using CMake without the toolchain file doesn't fail for trivial cases.
+
+This isn't something we expect to work well, but it is something people use, so we at
+least verify that the most trivial of builds succeed.
+"""
+import subprocess
+from pathlib import Path
+from tempfile import TemporaryDirectory
+
+from ndk.hosts import Host
+from ndk.paths import ANDROID_DIR
+from ndk.test.spec import BuildConfiguration
+
+
+def find_cmake_and_ninja() -> tuple[Path, Path]:
+    host = Host.current()
+    if host is Host.Windows64:
+        tag = "windows-x86"
+    else:
+        tag = f"{host.value}-x86"
+    return (
+        ANDROID_DIR / f"prebuilts/cmake/{tag}/bin/cmake",
+        ANDROID_DIR / f"prebuilts/ninja/{tag}/ninja",
+    )
+
+
+def run_test(ndk_path: str, config: BuildConfiguration) -> tuple[bool, str | None]:
+    cmake, ninja = find_cmake_and_ninja()
+    with TemporaryDirectory() as build_dir:
+        try:
+            subprocess.run(
+                [
+                    cmake,
+                    "-B",
+                    build_dir,
+                    "-S",
+                    ".",
+                    f"-DCMAKE_ANDROID_NDK={ndk_path.as_posix()}",
+                    "-DCMAKE_SYSTEM_NAME=Android",
+                    f"-DCMAKE_SYSTEM_VERSION={config.api}",
+                    f"-DCMAKE_ANDROID_ARCH_ABI={config.abi}",
+                    f"-DCMAKE_MAKE_PROGRAM={ninja}",
+                    "-G",
+                    "Ninja",
+                ],
+                check=True,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.STDOUT,
+                text=True,
+            )
+            subprocess.run(
+                [cmake, "--build", build_dir],
+                check=True,
+                stdout=subprocess.PIPE,
+                stderr=subprocess.STDOUT,
+                text=True,
+            )
+        except subprocess.CalledProcessError as ex:
+            return False, f"Build failed:\n{ex.output}"
+    return True, None