CMake incompatible with Android NDK r16 clang toolchain

When trying to build an Android project with NDK r16 beta 1 and the clang toolchain, the toolchain's paths are broken. This is a regression from the current stable release NDK r15c. It works when using the default GCC toolchain (which is deprecated in NDK and will be removed).

Here's a minimal example:

CMakeLists.txt:

cmake_minimum_required(VERSION 3.9)
project(CMakeAndroidTest)
add_executable(cmake-android-test main.cpp)

main.cpp:

int main() {
    return 0;
}

The following was run with CMake 3.9.1 on Linux x86_64 (Fedora 26).

NDK r15c, default GCC toolchain: works

$ ANDROID_NDK=/path/to/ndk-r15c cmake .. -DCMAKE_SYSTEM_NAME=Android
-- Android: Targeting API '26' with architecture 'arm', ABI 'armeabi', and processor 'armv5te'
-- Android: Selected GCC toolchain 'arm-linux-androideabi-4.9'
[...]
-- Build files have been written to: [...]

NDK r15c, clang toolchain: works

$ ANDROID_NDK=/path/to/ndk-r15c cmake .. -DCMAKE_SYSTEM_NAME=Android -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang
-- Android: Targeting API '26' with architecture 'arm', ABI 'armeabi', and processor 'armv5te'
-- Android: Selected Clang toolchain 'arm-linux-androideabi-clang' with GCC toolchain 'arm-linux-androideabi-4.9'
[...]
-- Build files have been written to: [...]

NDK r16 beta 1, default GCC toolchain: works

$ ANDROID_NDK=/path/to/ndk-r16-beta1 cmake .. -DCMAKE_SYSTEM_NAME=Android
-- Android: Targeting API '26' with architecture 'arm', ABI 'armeabi', and processor 'armv5te'
-- Android: Selected GCC toolchain 'arm-linux-androideabi-4.9'
[...]
-- Build files have been written to: [...]

NDK r16 beta 1, clang toolchain: fails

$ ANDROID_NDK=/path/to/ndk-r16-beta1 cmake .. -DCMAKE_SYSTEM_NAME=Android -DCMAKE_ANDROID_NDK_TOOLCHAIN_VERSION=clang
-- Android: Targeting API '26' with architecture 'arm', ABI 'armeabi', and processor 'armv5te'
-- Android: Selected Clang toolchain 'arm-linux-androideabi-clang' with GCC toolchain 'arm-linux-androideabi-4.9'
-- The C compiler identification is unknown
-- The CXX compiler identification is unknown
CMake Error at CMakeLists.txt:2 (project):
  The CMAKE_C_COMPILER:

    /path/to/ndk-r16-beta1/toolchains//prebuilt/linux-x86_64/bin/clang

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CC" or the CMake cache entry CMAKE_C_COMPILER to the full path to
  the compiler, or to the compiler name if it is in the PATH.


CMake Error at CMakeLists.txt:2 (project):
  The CMAKE_CXX_COMPILER:

    /path/to/ndk-r16-beta1/toolchains//prebuilt/linux-x86_64/bin/clang++

  is not a full path to an existing compiler tool.

  Tell CMake where to find the compiler by setting either the environment
  variable "CXX" or the CMake cache entry CMAKE_CXX_COMPILER to the full path
  to the compiler, or to the compiler name if it is in the PATH.

The correct path where clang and clang++ are located is /path/to/ndk-r16-beta1/toolchains/llvm/prebuilt/linux-x86_64/bin. Notice the missing llvm in the path used by CMake.