[CMake] Android NDK, clang, and ODR violations

[Christopher Broadbent]

I'm in the progress of updating some code to clang in the NDK (since 
they are not longer supporting GCC), and getting some ODR errors which 
seem to be caused by a bad link configuration.

The generated executables / shared libraries seem to link to both the 
selected standard library, and libstdc++.so (android's minimal 'system' 
standard lib, not gcc's c++ standard lib). This causes multiple 
definitions of new/delete, triggering ODR warnings between 'libc++abi.a' 
and 'libstdc++.so'

When using the gnustl_static, there's similar issues on the members of 
'std::type_info', 'std::basic_string', and 'std::shared_ptr', but this 
is now between our code and 'libgnustl_static.a' (possibly a clang vs 
gcc code gen difference?)

This happens in cmake 3.7.2 and cmake 3.8

Is anyone successfully using cmake + clang on android, or have an idea 
of where the configuration script might be wrong?

Here is my reproduction:

--- toolchain.cmake
set(CMAKE_SYSTEM_NAME       Android)
set(CMAKE_SYSTEM_VERSION    19)
set(CMAKE_ANDROID_ARCH_ABI  armeabi-v7a)
set(CMAKE_ANDROID_NDK_TOOLCHAIN_VERSION clang)
set(CMAKE_ANDROID_STL_TYPE  c++_static)
--- CMakeLists.txt
cmake_minimum_required(VERSION 3.7.2)
cmake_policy(VERSION 3.7.2)

project(reproduction)

string(APPEND CMAKE_EXE_LINKER_FLAGS " -Wl,--detect-odr-violations")

add_executable(main main.cpp)
--- main.cpp
#include <iostream>
int main() {
   std::cout << "hello, world!\n";
}
---

Thanks,


Chris