title: Android Studio ERROR: Cause: executing external native build for cmake /path/to/project/app/tools/CMakeLists.txt
body: <p>I have downloaded WireGuard from Github (<a href="https://github.com/WireGuard/wireguard-android" rel="nofollow noreferrer">link</a>) after run app by android studio I have this error:</p>
  
  <pre><code>ERROR: Cause: executing external native build for cmake  /path/to/project/app/tools/CMakeLists.txt
  </code></pre>
  
  <p>and <code>android_gradle_generate_cmake_ninja_json_x86.stderr.txt</code> show this:</p>
  
  <pre><code>    CMake Error at CMakeLists.txt:11 (add_executable):
      Cannot find source file:
  
      wireguard-tools/src/wg-quick/android.c
  
      Tried extensions .c .C .c++ .cc .cpp .cxx .m .M .mm .h .hh .h++ .hm .hpp
      .hxx .in .txx
  
  
      CMake Error: CMake can not determine linker language for target: libwg-quick.so
  </code></pre>
  
  <p>wireguard-tools folder is empty. maybe it's content must build by cmake from CMakeLists.txt.
  I don't understand cmake.
  CMakeLists.txt content is:</p>
  
  <pre><code># SPDX-License-Identifier: Apache-2.0
  #
  # Copyright © 2018-2019 WireGuard LLC. All Rights Reserved.
  
  cmake_minimum_required(VERSION 3.4.1)
  set(CMAKE_RUNTIME_OUTPUT_DIRECTORY "${CMAKE_LIBRARY_OUTPUT_DIRECTORY}")
  
  # Work around https://github.com/android-ndk/ndk/issues/602
  set(CMAKE_EXE_LINKER_FLAGS "${CMAKE_EXE_LINKER_FLAGS} -fuse-ld=gold")
  
  add_executable(libwg-quick.so wireguard-tools/src/wg-quick/android.c ndk-compat/compat.c)
  target_compile_options(libwg-quick.so PUBLIC -O3 -std=gnu11 -Wall -include ${CMAKE_CURRENT_SOURCE_DIR}/ndk-compat/compat.h -DWG_PACKAGE_NAME=\"${ANDROID_PACKAGE_NAME}\")
  target_link_libraries(libwg-quick.so -ldl)
  
  file(GLOB WG_SOURCES wireguard-tools/src/*.c libmnl/src/*.c ndk-compat/compat.c)
  add_executable(libwg.so ${WG_SOURCES})
  target_include_directories(libwg.so PUBLIC "${CMAKE_CURRENT_SOURCE_DIR}/wireguard-tools/src/uapi/" "${CMAKE_CURRENT_SOURCE_DIR}/wireguard-tools/src/")
  target_compile_options(libwg.so PUBLIC -O3 -std=gnu11 -D_GNU_SOURCE -idirafter "${CMAKE_CURRENT_SOURCE_DIR}/libmnl/include/" -include ${CMAKE_CURRENT_SOURCE_DIR}/ndk-compat/compat.h -DHAVE_VISIBILITY_HIDDEN -DRUNSTATEDIR=\"/data/data/${ANDROID_PACKAGE_NAME}/cache\" -Wno-pointer-arith -Wno-unused-parameter)
  
  add_custom_target(libwg-go.so WORKING_DIRECTORY "${CMAKE_CURRENT_SOURCE_DIR}/libwg-go" COMMENT "Building wireguard-go" VERBATIM COMMAND make
      ANDROID_ARCH_NAME=${ANDROID_ARCH_NAME}
      ANDROID_C_COMPILER=${ANDROID_C_COMPILER}
      ANDROID_TOOLCHAIN_ROOT=${ANDROID_TOOLCHAIN_ROOT}
      ANDROID_LLVM_TRIPLE=${ANDROID_LLVM_TRIPLE}
      ANDROID_SYSROOT=${ANDROID_SYSROOT}
      ANDROID_PACKAGE_NAME=${ANDROID_PACKAGE_NAME}
      CFLAGS=${CMAKE_C_FLAGS}\ -Wno-unused-command-line-argument
      LDFLAGS=${CMAKE_SHARED_LINKER_FLAGS}\ -fuse-ld=gold
      DESTDIR=${CMAKE_LIBRARY_OUTPUT_DIRECTORY}
      BUILDDIR=${CMAKE_LIBRARY_OUTPUT_DIRECTORY}/../generated-src
  )
  # Hack to make it actually build as part of the default target
  add_dependencies(libwg.so libwg-go.so)
  </code></pre>
  
  <p>project structure:</p>
  
  <p><a href="https://i.stack.imgur.com/lR4w8.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/lR4w8.png" alt="enter image description here"></a></p>
  
  <p>i'm using Android studio 3.5.3 and gradle 5.4.1 in ubuntu 18.04.
  NDK(side by side) , LLDB and CMake also installed. however I see this warning(not error) in event log : <code>NDK Resolution Outcome: Project settings: Gradle model version=5.4.1, NDK version is UNKNOWN</code> in all projects. even those that not using ndk.
  in local.properties I defined :</p>
  
  <pre><code>ndk.dir=/home/hadi/Dev/Android/android-sdk/ndk/21.0.6113669
  sdk.dir=/home/hadi/Dev/Android/android-sdk
  </code></pre>
  
  <p>Can anyone help me?</p>