It is #ifdef __ANDROID__ as seen by running the preprocessor:
~$ /usr/local/android-ndk-r6/toolchains/arm-linux-androideabi-4.4.3/prebuilt/linux-x86/bin/arm-linux-androideabi-gcc -E -dM - < /dev/null | grep -i android
The output is:
#define __ANDROID__ 1
No need to depend on defining stuff in your project especially if you’re skipping the NDK build system.