Discussion/Enhancement: Use ANDROID macro definition in AndroidAppender

[rockaport]

When building with the Android NDK it automatically adds a -DANDROID definition to {C/CXX}FLAGS and it can be used to nop calls to android_log on non-android targets.

Right now I'm building a library that sets up several appenders and I'm handling adding the AndroidAppender using the ANDROID definition shown below. It's a small point, but It would be nice to clean this up and push these conditions into the AndroidAppender. It would just be a nop if it's being run on a non-Android target.

I don't even think a compile warning is necessary if you're compiling in an AndroidAppender for a non-Android target.

I'm already handling the linking of plog/log using a cmake interface and there's two places I need to manage this. I guess this could get pushed into plog/CMakeLists.txt too?

# logger.cmake
add_library(logger INTERFACE)
target_link_libraries(logger INTERFACE plog)
if (ANDROID)
    target_link_libraries(logger INTERFACE log)
endif ()

# CMakeLists.txt
include(logger.cmake)
target_link_libraries(${PROJECT_NAME} PUBLIC logger)

// some-file.cpp
#ifdef ANDROID
#include <plog/Appenders/AndroidAppender.h>
#endif

void foo::initLogger() {
    plog::init(plog::debug);

    static plog::ColorConsoleAppender<plog::TxtFormatter> colorConsoleAppender;
    plog::get()->addAppender(&colorConsoleAppender);

    #if ANDROID
        static plog::AndroidAppender<plog::TxtFormatter> androidAppender("app");
        plog::get()->addAppender(&androidAppender);
    #endif
}