__ANDROID__ is the correct macro to check for an android system.ANDROID is only defined in NDK build system (.mk) and not in the standalone NDK.

src/file/SDL_rwops.c

@@ -38,7 +38,7 @@
 #include "cocoa/SDL_rwopsbundlesupport.h"
 #endif /* __APPLE__ */
 
-#ifdef ANDROID
+#ifdef __ANDROID__
 #include "../core/android/SDL_android.h"
 #include "SDL_system.h"
 #endif
@@ -466,7 +466,7 @@ SDL_RWFromFile(const char *file, const char *mode)
         SDL_SetError("SDL_RWFromFile(): No file or no mode specified");
         return NULL;
     }
-#if defined(ANDROID)
+#if defined(__ANDROID__)
 #ifdef HAVE_STDIO_H
     /* Try to open the file on the filesystem first */
     if (*file == '/') {