The objects in this prebuilt directory can be rebuilt from the source in
$ANDROID/external/qemu/distrib/sdl-1.2.15.

For 32-bit
$ cd $ANDROID/external/qemu/distrib/sdl-1.2.15
$ ./android-configure.sh --prefix=$ANDROID/prebuilts/tools/linux-x86/sdl
$ make
$ make install

To add 64-bit *.a (after successful 32-bit build)
$ cd $ANDROID/external/qemu/distrib/sdl-1.2.15
$ ./android-configure.sh --try-64
$ make
$ cp objs/libs/libSDL.a $ANDROID/prebuilts/tools/linux-x86/sdl/libs/lib64SDL.a
$ cp objs/libs/libSDLmain.a $ANDROID/prebuilts/linux-x86/sdl/libs/lib64SDLmain.a