1. Set CMAKE_FIND_ROOT_PATH unconditionally.
Revise the implementation from commit a7f41a7ee4 (Android: Fix find_*
search order within NDK for unified toolchains, 2020-10-13). In the old
implementation, if people set CMAKE_FIND_ROOT_PATH, CMAKE_ANDROID_NDK
won't be added to find root. And all paths added to CMAKE_SYSTEM_*_PATH
below will be rerooted to the user specified root.
2. Add api level specific library path to CMAKE_SYSTEM_PREFIX_PATH.
As the discussion in [1], some people want the paths added by
UnixPaths.cmake. They install their libraries according to
GNUInstallDirs [2].
As a result, we cannot clear CMAKE_SYSTEM_PREFIX_PATH. It includes /usr
so no matter what we specify in CMAKE_SYSTEM_LIBRARY_PATH,
/usr/lib/<arch> will be searched first.
The author also pointed out a way to solve this issue [3]. In addition
to other paths, CMake also searches <root>/<prefix> [4]. So we can add
the API specific lib path to the beginning of CMAKE_SYSTEM_PREFIX_PATH,
to have it searched first.
[1] https://android-review.googlesource.com/c/platform/ndk/+/1486800
[2] https://cmake.org/cmake/help/latest/module/GNUInstallDirs.html
[3] https://github.com/android/ndk/issues/1179#issuecomment-613435081
[4] 11425041f0/Source/cmSearchPath.cxx (L202)
NDK r18 drops GCC toolchains and some STL types. We need to choose a
clang toolchain by default when no gcc toolchains are available. Switch
the STL type default to `c++_static` when the old `gnustl_static`
default is not available.
Update the test suite to not run tests for STL types that do not exist.
Also do not expect the gcc toolchain `cpp` tool to be available because
r18 does not provide it. Also teach it to tolerate `gcc -dumpmachine`
output like `arm--linux-android` that differs from the toolchain prefix.
Fixes: #18301
The `armeabi` ABI is no longer available, so we can no longer use it by
default unconditionally. Instead detect all available ABIs and choose
the oldest arm ABI that is available.
Also update the test suite to account for the lack of `armeabi` support
and pass as of Android NDK r17-beta2.
Add missing "unwind" and "atomic" libraries needed for this combination.
See `${ndk}/sources/cxx-stl/llvm-libc++/libs/armeabi/libc++.a` for the
libraries the NDK uses.
Issue: #16380
