moc_predefs.h do not contain __ANDROID__ with clang (NDK) anymore (missing target)

We use cmake to generate moc_predefs.h for Qt5 and his moc binary.

Since we switched to clang compiler with Android NDK we see that it does not provide __ANDROID__ anymore.

$ /opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ -dM -E -c /usr/share/cmake-3.12/Modules/CMakeCXXCompilerABI.cpp

[...]

$ /opt/android-ndk/toolchains/aarch64-linux-android-4.9/prebuilt/linux-x86_64/bin/aarch64-linux-android-g++ -dM -E -c /usr/share/cmake-3.12/Modules/CMakeCXXCompilerABI.cpp

[...]
#define __ANDROID__ 1

Looks like cmake misses to pass the target to the clang.

/opt/android-ndk/toolchains/llvm/prebuilt/linux-x86_64/bin/clang++ -dM -E -target aarch64-linux-android -c

https://github.com/android-ndk/ndk/issues/807