__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.

include/SDL_egl.h

@@ -420,7 +420,7 @@ typedef struct gbm_device  *EGLNativeDisplayType;
 typedef struct gbm_bo      *EGLNativePixmapType;
 typedef void               *EGLNativeWindowType;
 
-#elif defined(ANDROID) /* Android */
+#elif defined(__ANDROID__) /* Android */
 
 struct ANativeWindow;
 struct egl_native_pixmap_t;

include/SDL_rwops.h

@@ -93,7 +93,7 @@ typedef struct SDL_RWops
     Uint32 type;
     union
     {
-#if defined(ANDROID)
+#if defined(__ANDROID__)
         struct
         {
             void *fileNameRef;